Here’s the thing. The DSi is crazy, but I got a new DS Lite over summer and I think it’s way too soon to switch over to a new handheld (besides, the Lite is still awesome). So I told myself that once they make a new handheld that doesn’t use DS games, then I’ll get it (I mean, it could be DS-compatible, but I’m talking about a new cartridge they’re using).
Here’s a timeline to give you an idea of what Nintendo usually follows:
Gameboy Color 1998
Gameboy Advance 2001
Nintendo DS 2004
Nintendo DS Lite 2007
Nintendo DSi 2009
(note: of course not everything is in the timeline)