I change the engine oil at 3000 mile or 3 months which ever comes first. The transaxile is required at 100K, but other users strongly suggested at 60K. I have no problems at 106k without a change (it will be performed very shortly).
The attached link shows a discussion I found among die hard prius users and mechanics which sheds some technical parameters and specifications to those of interest in engineering details such as viscosity and molecular break down, etc....
Yahoo! Answers - Search
I think the dealer is trying to upgrade (oversell) their services. The best way out is by helping each other as owners and learning the facts from myths and arm twisting sales tactics.
If one likes to learn more about the Prius, one may probably want a subscription to:
1.
http://techinfo.toyota.com/ (US and maybe Canada)
Toyota Publications... (Europe/UK and maybe Australia)
where if you have the patience, a credit card, and a fast Internet connection, one can download the repair manuals, electrical wiring diagrams, etc. as much as you want within your subscription window.
You may also want to read through the Toyota technician training courses for the Prius at:
http://www.autoshop101.com/autoshop15.ht...
http://www.autoshop101.com/autoshop15.ht...
Visit links of interest for a repair technician available at:
toyo : socios
Good luck,
Km