After downloading a registering app onto your PSP, you can register UMDs to a specific PSN account, and then, if the developer of that game has allowed it, you can pay a fee (ranging (at this time) from ¥500-1500 (per game)).
This is better than nothing, and probably the best Sony could do; the games are the developers’, and if they don’t want people to be able to copy them, that’s their right. Not all developers have agreed to make their games available, either.
Any PSP games bought through the PSN are already compatible with the PS Vita, no hoop-jumping required.
I imagine most people will keep their PSPs around for their old games; if you’ve got a big library of games, it could cost you quite a bit to make them all PS Vita compatible. For a few select games, though, it would make more sense.