You also realize that the 3ds is immensely more powerful then the DS when it comes to specs, even without the 3d processing, and that the 3d aspect is not at all required for developers publishing to the 3ds.
The engine for 3ds games, and the format they are in are completely different. Yes they borrow elements from the game format and builds that they used with the DS because it worked well, but its still vastly different.
The 2DS is cheaper because they removed so much technology, but is still incredibly more powerful then a DS and it needs to be because of the games that it will be required to run, and they wanted a console that was a lot cheaper to help boost the sales, because they screwed themselves over by releasing the 3DSXL so early.
Saying that they are the effectively same system is like saying the PS2 is just an upgraded PS1. Very different when you get down to the technical side of it