The Prius does not cost less
The Prius does not cost less to maintain, it is just that Toyota has decided to eat the cost of that maintenance for the first few years. If you compare the first 5 years of maintenance instead, I bet the Prius would cost more, or at least the same. Regardless, the only reason you can say that the Prius costs less is because Toyota, in an effort to win/retain customers (especially after all its recall troubles) has thrown in free maintenance. Its a gimmick. You should make it a point to explain WHY the cost is less and not just state that it is less John, especially because if one buys the Prius and keeps it for longer than the free maintenance period, they will be paying more in maintenance.
As for depreciation, you're absolutely right. I wonder if, after the rebates are gone in a few years, for the LEAF, if it will be a different story though.