And why couldn't they release those games also on Nintendo platform(s), if Sony ones can't be as profitable as in the past anymore? I know the scenario I'm talking about is quite extreme, but Sony's future in the handheld future could take an extreme route (no traditional handheld anymore), so I guess it's not impossible to speak about that in these terms.
Given the the fact that smartphone penetration is expected to go from 30% in 2012 to >80% in 2017, I wouldn't count on the audience for dedicated handhelds to remain the same. I think we have to come to terms with the fact that the pressures that are killing Sony's handheld division do affect Nintendo and 3rd party software developers as well.
Further, Sony exiting the market does nothing to address the underlying profitability of 3rd party developers. In fact, it hurts them because they are forced to deal with a single corporation who now has the power to squeeze them if they want to release software for a dedicated handheld. eg. What kind of deal is Capcom going to get for MH5 if there is only one place they can release it vs MH4? Maybe that is why they are hedging by investing MH profits into a mobile studio instead of beefing up their dedicated unit(s).