A long time ago i posted a thread regarding the PSP screen possibly not being true 16:9 format, well... and this is probably pretty stupid to post, but a bit more evidence that this is really the case...
When you start up the Spiderman 2 movie included with the Value Pack, it says "This move has been modified from it's original version. It has been formatted to fit this screen." In every case it's ever been used, this sentence applies to changing the screen ration of the original (16:9) to fit... well usually, a 4:3 TV screen. So in this case it must mean that they had to edit/crop the picture at least a little bit to fit the screen... hence, the PSP screen must not be true 16:9... which is probably why I had such a hard time getting movies (DVD rips, true 16:9) to show up when run from the memory stick w/o them appearing slightly squished vertically.