Not all plug-in vehicles are created equal. As we finally start to see mainstream, commercially available plug-ins arrive, the market is developing into a continuum. At one extreme we have the pure battery electrics like the Tesla Roadster, Nissan Leaf and Ford Focus Electric. Somewhere in between we have the extended range electric vehicle as personified by the Chevrolet Volt. At the other end we, have the conversion plug-in hybrid (PHEV) such as the prototype Ford Escape PHEV and Toyota Prius PHEV.
Just as sub-compact cars and full-size SUVs appeal to different customers, each of these types of vehicles have quite different capabilities and are suited to divergent use cases. As Toyota continues to deploy its test fleet of plug-in Priuses, it is making the case that the car is not a direct competitor to the Leaf or Volt. Instead it sees this as a "Prius Plus" with the same basic functionality but better efficiency (that's pretty much what we experienced, too). Since the Prius and other PHEVs are not really designed for pure electric driving, Toyota wants people to look at the percentage of electric driving rather than the straight electric range. These little differences in marketing and vehicle capability will make it very interesting to watch the plug-in market develop over the next several years.