I mentioned this to the Tesla dealer in Washington Square (Portland, OR) yesterday, he suggested I post it on the forum.
The cars used for test drives are all performance models - until dealers get a "regular" car, there's no real way to feel what the differences are between performance, regular 85 kWh, 60 kWh, etc. Reading the performance numbers isn't' the same as "feeling" it.
It seems to me that it would be possible to put in an emulation mode switch via software - that is, you have a performance model, but it can be made to emulate a lesser model's performance by changing a setting.
This accomplishes several things - it lets the dealers only need one type of car (air suspension notwithstanding), and allows potential customers to feel the difference in performance. I know some folks I've talked to are reluctant to buy a car if they've only been able to test-drive a souped up version, not the one they'd actually get.
There's a potential for up-selling, too - if someone thinks the regular 60 or 85 kWh pack is fine, letting them see what they're missing by not getting the performance model might get them to upgrade.
This assumes, of course, that the acceleration of the car is controlled by software, but I think that's a pretty safe bet.