There was a post here with a source, but I can't be f***ed finding it. Instead, I found you a nice link from Google, which you should have just done yourself. Here's what it says:
Nintendo of America’s DSi announcement also casually mentioned there is more to the DSi than the camera and DSiWare. In case you didn’t catch the blip here’s the skinny.
In addition to downloadable games, Nintendo DSi is able to play games made specifically for the system and sold at retail. The system can also play most Nintendo DS™ games, and will have access to a library of more than 850 titles originally made for that system.
A few months ago PM Studios told us they were working on making a DSi version of DJ Max Technika. Their plan is to give the Nintendo DSi release more features, but DJ Max Technika would work with a regular DS too. Hardware publishers can take advantage of on the DSi include the camera, faster network connections, the DSiWare Store, and storage space on an SD card.
And is it not obvious that there are going to be exclusive games? Why else would Nintendo QUADTRUPLE the RAM, up the processor speeds, and add 2 cameras amongst other things? Perhaps for new, better games that the DS and DS Lite just could no handle? Oh, and hey! I heard the PSP2 is coming out, but they're not making PSP2 games, just more normal PSP games. It's all just a big con to get people to spend more money! Using the potential of a better console to have better games - what a dumb ass idea that is!
Seriously, just think about it.