I guess the concern is that the DSi might just be like the GBA Micro. Now, the GBA SP definitely made sense because it was a huge advance over the original GBA, and it came out early enough to be worth getting... but if I'm not mistaken, the GBA Micro actually came out after the DS was released, so that really made no sense, and I doubt Nintendo recouped their development cost for that because so few actually sold. I mean the Micro was a cute idea and a nice thing to have, but if you had an SP or DS it wasn't really worth it.
At least the DSi is coming out before the DS2, so that's something, but on the other hand the DS2 may be only be a year or two off.