I always buy new Mario games but don't want a 3DS. Will Super Mario 3D Land work at all on the old DS or any chance of a similar title being released for that console?
Ah, but this comparison is fundamentally flawed. You can turn off the 3D effect on the 3DS, you can't on a 3D movie (in theaters, at least) without special glasses or some such.
Sorry, if I could play 3DS games on a DS/DSi and I didn't care about the 3D effect, why in the world would I (or anyone of a similar disposition) buy a more expensive 3DS? It wouldn't do anything the DS couldn't do if that were true.
The 3DS is more powerful than the DS, so games are written to take advantage of that power.