That's kinda why I was suggesting something that would allow a limited ammount of re-encryption by the end user; hopefully sufficient enough that if things go wrong for GPH, the game will continue to work unless you go through a ridiculous number of units.
Alternatively, you could encrypt a game to an individual user... by which I mean you (the user) would supply about 40 questions about yourself, each multiple choice, along with the answers, and some dummy answers. Then, roughly every 5 times the program ran, it'd display the user data (This program is for the use of X only), and ask you 1 or 2 questions from the batch... if you got it wrong, though, being multiple choice, you'd need to get 10 right (in a row), and if still went bizarre, the software would do the mobile phone thing of locking itself until you'd got an unlock code from the developers.
Could be a little harsh; I don't know. Maybe have it display a message like "please give this GP2x back to the original user to answer the questions" before locking it, but the idea is somewhat sound... no different really than a mobile phone sim card though.
The result of this is that the game could run on any GP2x or SD card, but only be run by one person, unless they supplied the database of answers (similar to, for those of you who remember, copy protection systems that required you to tell the program what word was on page 7 line 6 of the manual).
The challenge would be to make the database sufficiently large without making it too much of an effort to buy something. But if a standard were developed for the db format such that it could be used with any piece of software, then it might not be too much to expect a buyer to go through once and never again.
Even displaying user data on launch might be a bit of an incentive not to share... certainly it works for beta testers - you instantly know who shared their beta, and so you can vow never to supply one again to that person.
Perhaps that sort of thing would work... you could have a DNR (do not run) list of GP2x IDs, such that if your piece of software gets passed on, no piece of commercial software will work on your GP2x again (i.e. rather than checking and only running if it is a given ID, it checks and if it finds your ID among the list that it won't run on, it crashes).
It'd be a bit harsh to those who bought second hand GP2xes from anuses who had managed to get their units ONTO the DNR list, but that's life... perhaps it could be taken off (or at least put on parole) for a suitable fine.
Just a couple of other ideas, anyway