Not necessarily, you're assuming that every game on the NGP will be super high-end, which is most certainly not the direction the handheld market is going...in entirety. There's a huge market for smaller games (to pass the time), as well as for bigger games. Sony and Nintendo both enjoy a huge internal development team so both systems will be supported internally pretty handily.
With Indie devs though, Sony has a 'we pay your dev costs' project, that helps bring them to the fold. Yes, it's exclusive, but with the NGP and PS3 capable of playing virtually the same games, it'll make PSN that much more attractive a platform to launch from for indie devs.
It's going to boil down to ease of development with the architecture of the device, I think. The biggest hurdle for Sony lately has been that the PS3's architecture starts it well behind other General Purpose CPU/GPU setups that most software developers are accustomed to this day and age. If it's exactly like, or quite similar to the PS3, then most devs should already have a handle on that. If it's something altogether new, that could present an issue.
Though, it should also be mentioned that Sony's definitely been keeping devs in the loop with their designing of this device, far more than they did with the PS3. Either way, I'm pretty psyched about the cross-platform potential between the PS3/NGP. And there are plenty of PSN games I'd prefer to have as a mobile app.
