I think what happened is that a bunch of developers walked out of Avatar convinced that the 3D was the next big thing and wanting to hop on the bandwagon ASAP.
That's only 6 months of development time, so probably not. The more likely explanation is that developers just think the system will do well. Remember, the PSP had 30 launch titles in the US (which I think might be a record for any US system launch?) If you're developing a game, obviously you get a choice of "do we make this a DS title, or a 3DS title?"--and while DS titles will hit a wider install base, early 3DS titles will get a lot of mindshare from, say, people on the internet reading a "games in development" list. (Kinda like how Monkey Ball hit fairly mainstream purely because it was a GameCube launch title, whereas Monkey Ball was an obscure non-seller before then).
And developers can be wrong; developers had more faith in the PSP than the DS. 3DS feels like a pretty safe bet, though (new Nintendo portable successor to the best-selling system of all time. Main update this system is that the graphics are shinier. Yeah, feels pretty safe).
