As far as I understand pirated games are not really hacked yet. Just the environment they run in redirects the loading to the mem stick.
Some of the games use fake data to make the image larger, but nobody seem to check if the data is really there. So you can just delete that data or movies (just replacing with dummy files) from the ISO. But if the games would use the whole 1.8 gig of an UMD and acutally check if the file sizes are unchanged at least we all would need 2 gig sticks to play pirated games.
One step further, it actually shouldnt be that hard to check if data is loaded from a mem stick or from a drive (which ovbiously takes longer).
With that extra security games could then allow gamers to install content on the stick for faster load times (and less battery strain). This could in many cases easily be the whole game code or at least some data thats frequently used.
Or did I get something terribly wrong?