I personally think it is because of the EPA's corrected mileage estimates. For example, the Prius goes from 61 MPG to 45 MPG. I am guessing that if a 45MPG Prius is sold next to a "61 MPG" Prius, Toyota is going to have a lot of problems.
Actually, most are out in September to October timeframe.
The plants traditionally shut down in July for 2 weeks and changeover models at that point. They then need to run for awhile to build an inventory before the marketing push really begins.
Of course, you do see a trickle of models early, and there are always the new ones out in January...
For example, Ford began selling the 2008 Taurus in late June. There still aren’t enough out there to justify a big marketing push yet, though. The 2008 Escape, 2008 Escape Hybrid, and 2008 Super Duty are all on sale now as well.
I always thought that the mpg ratings were for comparison only, and that everyone knew you never got what was shown on those ratings. I just got past 90,000 miles on my 2005 Prius (purchased in 11/04) and my average mpg is around 49.5. Some tanks much better (recently had a 53 mpg tank for around 500 miles driven), few tanks less than 48 mpg. Compared to my last car, a VW Passat 4 cylinder turbo (24 mpg overall on premium gas), I am doing well.
I do have to re-educate people who think I am “green.” While I don’t try to harm the environment, for me buying the Prius was about saving gas and having a “gadgety” car to play with, since I am in it so much. My wife really likes it, too. It is easy for my kids (15 year olds with learners’ permits) to drive. I never have to take the key out of my pocket. The lights turn off when you get out of the car. It is just a fun, economical car.