@Michael - I'm not saying that the Prius plug-in technology itself is a major development. Yet, the fact that consumers won't just have the single choice of a Volt-like system--which granted allows for exclusive use of electric propulsion for 35+ miles--but also a Toyota system that is probably going to be priced about $10,000 less than the Volt...that's major. Also consider that the Prius is more spacious.
If you consider that more drivers will use ALL of the electric capacity at 13 miles, and that a fair amount of the time, Volt drivers will come home with juice left in the 16 kWh/35-mile-pack, then you could argue that there's less waste of battery capacity/cost.
From a market perspective, you could also argue that some folks shopping for a gas Prius, might spend a couple thousand more to upgrade to the plug-in version. Considering the scale of Prius production, the lower cost of the Prius PHV versus the Volt, then more total miles on electricity could get chalked up to the Prius versus the Volt.
I don't mean to suggest that it's an either-or. It's great that both varieties of plug-in hybrid are going to be in the marketplace. That's the cool thing. You might view the Prius-style of plug-in hybrid as underwhelming, but again, it's going to be significantly less expensive, not to mention quicker to charge--maybe even small enough of a battery to be fine with Level 1.
Keep in mind that Honda is also developing a plug-in hybrid system, with I believe a 5 or 6 kWh pack. So, we are going to see small and large battery PHEVs. Each consumer will need to figure out which is the better technology/value for them.
I don't see how this is a "major development". It only goes 13 miles on a charge, which is hardly worth the bother to plug-in. It also only has a top speed of 60 mph in electric mode, which is just fast enough to get you mowed down on an L.A. freeway.
The Volt I would consider a major development (although its range is just barely worth the bother of plugging in). This I consider underwhelming.