I fail to see what exactly is so exciting about this. I have a first-gen DS with most of the AAA titles for the system and I think I've played Snake on my iPod 3G more than I've bothered with anything on the DS in the past year.
The answer is that Activision is not likely to ever port Guitar Hero to the DS again and will likely scare off whoever else tries something 'clever' with Nintendo's devices because Nintendo will probably just shift the spec out from under them again.