Am I right that tart pans are not greased/buttered? Why not?

Ditto the above. However, I find that some shortbread crusts that you press into the pan rather than rolling out will stick if the dish is not buttered.

Assuming you're making a pastry-based tart, the pastry itself has enough butter/fat to ensure it doesn't stick to the pan. It will also contract a touch when baking (hopefully not too much!).

I think you're correct, because the crust (pate sucree probably?) has so much butter than it's not necessary. But that's just my hunch.