Because GM wants to make sure you don't have a "thermal incident" while you're doing 65 mph on the highway:

http://www.sacbee.com/101/story/927646.html

Article goes over some hybrid busses that were purchased by the city of Elk Grove, CA that had a nasty habit, of, ohhhhh....catching on fire.

Even if the Volt used tiny lead acid batteries the car would take 3 years to reach volume production. It's a completely new electrified platform and that takes a lot of time. Even a standard ICE platform takes that long and longer! If you think the other engineers are standing around waiting for the battery you are dreaming! They are running at more than full speed and assume the battery will be ready to plug in when the time comes. No time to waste!

Ford dosen't realize that 5 to 10 dollar a gallon gas will bankrupt them. They also betting their hydrogen fool cell will be viable in a few years. All I can say is I hope the free market goes towards BEV;s.
They foolishly think they can wait till 2012 to sell a plug in hybrid, by then 10 buck a gallon gas will forced them out of business Here is an excerpt from the web from Ford.

Ford plans environmentally friendly future
Graeme Fletcher, National Post
Published: Friday, May 09, 2008

Ford has laid out its plan to ensure a sustainable transportation future and a cleaner environment. The plan involves three steps. The near-term runs from now to 2012, the mid-term extends to 2020 and the long-term takes care of 2020 and beyond. It is an all-encompassing vision that touches all emerging technologies.

Greg Franette, chief engineer for Ford's fuel cell and hybrid vehicle programs, said the greening of the company's fleet would continue despite Ford's precarious financial position.

One of the statistics used in Mr. Franette's presentation was eye-opening: According to a 2006 report by Environment Canada, passenger cars and light trucks account for 12.5 per cent of the growing greenhouse gas problem, not the 25 per cent often touted. Industries, by comparison, account for 42 per cent, yet they somehow manage to escape close scrutiny.




In the near term, Ford will begin to roll out its EcoBoost range of four- and six-cylinder engines. The adoption of gasoline direct injection and turbocharging improves fuel economy by 20 per cent or more while dropping carbon dioxide emissions by 20 per cent without diminishing overall performance.

Next year, Ford will roll out an updated Escape Hybrid with a new 2.5L Atkinson-cycle engine in place of the current 2.3L four and will add a hybrid version of the Fusion.

As early as 2012, Ford will introduce a plug-in version of the Escape Hybrid. Replacing the current 330-volt nickel-metal-hydride battery with a lithium-ion pack and then charging it from the power grid allows the sport-utility vehicle to cover its first 64 kilometres on electric power alone. On a typical drive -- most daily commutes are less than 64 km -- the environmental impact would be massive.

For the long term, Ford is betting on the fuel cell. The company has 30 Focus fuel cell vehicles in operation in North America. In all, these test mules have amassed more than 1.2 million kilometres without significant problems.

In fact, Mr. Franette says the fuel cells have been very reliable, with only one being replaced to date. It is the ancillaries that are proving to be suspect -- the simple motors and pumps one tends to take for granted.

The latest expression of the fuel cell breed is Ford's HySeries Drive, which is making the rounds in a modified Edge. The system is a plug-in hybrid that uses a fuel cell in place of a conventional engine. As with the Escape, the HySeries Edge operates on the power stored in its 336-volt lithium-ion battery for the first 40 km of the drive. As soon as the main battery drops to a 40 per cent state of charge, the fuel cell fires up and begins to recharge the battery. This extends the driving range to a credible 360 km.

The Edge's packaging is straightforward. There are two 65-kilowatt (87-horsepower) electric motors (one front, one rear) that combine to add all-wheel-drive, plus a centrally mounted hydrogen tank (holding 4.5 kilograms) flanked by the battery pack and fuel cell stack.

As with a conventional hybrid, the HySeries also uses regenerative braking to capture the vehicle's kinetic energy while coasting or braking. This combination brings an equivalent fuel economy of 5.7 litres per 100 km. The HySeries is emissions-free, the only by-product being water.

The lone drawback in the HySeries Drive Edge is its mass. At 2,450 kg, it is, to be polite, rather rotund. With time, the weight problem will be addressed, which will increase the vehicle's driving range and overall performance.