The deciding factor on the tax rebate is who ends up owning the car...if you as the individual purchase the car, you can get the full tax credit. If you lease it, the leasing company does not get a $7500 tax credit, it's smaller, and you are getting a credit for that smaller amount...the dealer isn't making money off of it (at least as I understand it). The tax credit was intended to benefit the purchaser of a qualifying vehicle, and with a lease, that's not you!
Now, there is some talk about increasing that to $10K, but the way the bill is currently written (it's not passed as far as I've heard), it is capped at a certain dollar amount and I think the i3 and the Cadillac (Volt clone) are above that cap, so the current limit of $7500 would still apply.