I think a 60k+ debut for GTA might not seem too enthousiastic! But given the legs that are so common on Nintendo platforms nowadays it might still crack a million in that region! We all know GTA has a strong brand name, and that games are able to maintain steady sales in the others region with such a debut for the DS (and Wii). So I'm guessing this might be a hit in the long run, not so much for the debut. But that was the same for a lot of games!
Also; I think we can expect a 80-110k debut in the US! And given the userbase of the DS, GTA brandname etc... It will definitely be able to reach 2.5 million worldwide! Satisfying Nintendo, the public and Take 2 (Rockstar). I believe they (Rockstar) know all too well that this game wouldn't debut to more then 200k sales, but I guess they gambled on the legs. And I believe they gambled right.
And one more thing; Take 2 and Rockstar have to be financialy healthy. In order to accomplish such a thing for every fiscal year they will have to get somebig hitters out on the Nintendo platforms too! And there's no better way for paving the succes of the GTA franchise on the Nintendo platforms then releasing a DS version! Potentially with a succesor in 1.5-2 years which will follow the same sales patern only elevated by 1.5 (that's at least what I hope).
Thus paving the way for a split in the GTA series. One on the HD consoles and one on the Nintendo platforms!