Its a very good question and Eurogamer have created a video that tries to answer it. I quite like some of the reactions from the first party devs to this and its very interesting how they are trying to show that the PSVita is much more than your typical handheld and more like a console.
When it comes to mobile phone games taking part of the handheld market Sony reacts with some rather interesting comebacks.
Other interesting news on the PSVita front is that Sony today defended sticking with its proprietary memory cards on the PSVita. It’s not just to save data on but is to also combat piracy, which was a huge problem on the PSP.