That same thought occurred to me’
I would assume the 50 mpg is obtained by recovering regeneration energy during deceleration which would otherwise be dissipated as heat when braking a car with straight ICE drive and transmission
They have to store this regeneration energy somewhere, hence the battery
the minus side of course is the expensive battery which weighs 400 lbs and occupies space, and battery maintenance which is still an unknown factor.
How many persons could afford/would purchase a car transporting 4 persons for 40 thousand dollars?

I am addressing only this part of your comment. How did you arrive at this conclusion?
Here in Jacksonville Fl regular gasoline with about 10 percent alcohol retails for $2.60 I estimate the energy content about 35 kwh per gallon of the mixture (I may not be accurate, if so, please correct
0.9 gal regular gasoline = 0.9 x 125,000 =112,500 BTU
0.1 gal ethanol = 0.1 x 84,000 = 8,400 BTU
Total energy content of mixture =120,900 BTU =35.4 kwH
GM says it uses a 1 litre turbo charged gasoline engine, I don’t know its efficiency, let’s assume 0.30 also a generator eff of 0.92
Combined eff = 0.28
output = 9.8 kwH per gallon of mixture @ $2.60
Cost per kwH from the ICE = 26.6 cents
I paid 12.83 cents per kwH on my last bill, the ratio is about 2:1
As an aside, an article in our local paper quoted MrHenderson ceo of GM as stating that “the cost of charging the Volt is about 40 cents a day at 5 cents per kwH” That’s for 8 kwH driving 40 miles.
1 cent a mile!!!!
I assume Mr Henderson has solar panels on his roof or GM pays his electric bill.

The ICE generator would be smaller and less polluant using a Bio-Diesel type and finally the Lithium-Ion batteries would be replaced with Dr. Cui newest technology called the Silicon Nanowire Battery which holds 10 times the charge of existing Li-ion battery and will be a lot cheaper.

“Okay, this may be a dumb question, but if the depletion point is 30%, then is the all electric range somewhere around 28 miles” A wise man once said “There are no dumb questions, just dumb answers”. From the beginning, the Volt plan was to get about 40 miles of driving from 8 Kwh, or half of the 16 Kwh battery pack. So it still gets 40 EV miles before reaching the depletion point at 30%. Tests have discovered that for this type of LiIon battery, getting the State of Charge above 85% or below 20% puts stress on the battery and shortens its life. Thats why GM chose the 80% to 30% SOC scheme, it maximizes battery life and reliability.

“will only a certain segment of the battery pack be charged (to 80%, for example) by the generator to run the wheels, leaving the other plug-in segment of the battery pack at 30% to preserve the life?” No, the entire battery charges and discharges at the same rate and to the same amount. There are even special circuits to keep all the individual cells that make up the battery at the same charge level, making sure no cell in the pack gets fully charged or excessively discharged. Designing it so different parts were at different charge levels would introduce a lot of major headaches for no good reason, and probably cause premature failue of certain parts of the battery pack.

“Take this scenario. There are three segments of the battery pack. 1. Plug-in only 2. Generator only, 3. Regenerative braking only, only releasing energy once 80% charge is reached. This would reduce the number of charge cycles each battery cell would see. Does anyone see a problem with this scenario?” Major problem. It is unnecessarily complicated, and one of those segments would inevitably get used much more than the others and fail much sooner. Someone who had a short daily commute would wear out the “plug-in only segment” long before the rarely used “generator only segment”. Besides, a single pack can handle all three functions without any problems.

“Does, for example, every minute charge through regenerative braking or a larger charge resulting from the ICE running have the same effect upon the battery as one that would take the 30% SOC to 80% SOC?” No, two half discharge/charge cycles aren’t the same as two full discharge/charge cycles, in fact, counts for sligtly less than one! Minor charge fluctuations hardly matter at all.

“Is the generator always directly linked to the wheels or does it only supply power once the CDP is reached?” The generator is directly linked to the IC engine, and produces electrical power when the ICE is running. Electricity powers the motor that drives the wheels, and that electricity can come from the generator and/or the battery. During regenerative braking or when the generator is producing more power than the motor needs, the surplus electricity can go to recharge the battery.

“Will the Volt dump the generators excess power or will it adjust the generator output to match the cars needs?” Most of the generator output goes directly to the motor powering the wheels, and any excess goes to charge the battery. Once the SOC reaches a sufficiently high level, about 40%, the generator can shut off and the car resumes EV mode driving. But the power output of the IC engine and generator can be increased if necessary, like on the proverbial “going up a steep mountain pass while towing a trailer”, although the fuel economy would drop a bit.

“I am curious if the generator is A.C. or D.C.” Most likely AC, as varying output frequency really isn’t a problem here, it can easily be rectified to DC, and AC generators are usually brushless and need less maintenance.

“I think the biggest problem the Volt will have is stale gas..” That problem has already been solved, by the use of a sealed bladder style tank. The problem with gas going bad with age is caused by evaporation of ligher components, oxidation, and contamination, and a bladder tank keeps out air and prevents all of those causes.

“Sounds interesting, but I heard it’s better for batteries to charge them up, then almost totally deplete them before charging them up again.” That is only true for NiCad batteries, due to a NiCad phenomenon called “memory”. It is NOT TRUE for lead acid, NiMH, or any kind of LiIon battery, and for all of those battery types, deep depletion will shorten their lifespan, and they don’t suffer from the memory effect.

This is not so, it actually hurts the battery when you get close to 0%.. it will kill the battery if kept at 0% for a couple of days. Toyota is even more careful with the Prius battery than GM is with the Volt’s.. Edison’s old Nickel-Iron batteries are the only ones (that I know of) that will take any abuse, some are still working after 100 years.

Also good; allow for an out-of-gas and out-of-battery mode, where a user could deplete past the “I’m empty” 30% mark (perhaps to 10 or 15%) in sort of a limp-in mode to get to a gas station or plug-in.