I don't know for sure, but I suspect one issue is the fact that even if it can be modified to play, say a Region 2 PAL source, it may not convert PAL to NTSC. ie. It will play the PAL disc, but as PAL. Assuming that is true, you're still SOL, since the vast majority of North American TVs freak out when fed a PAL source.
In places where a lot of region free DVD players are sold, this is still a big issue. Whereas systems which convert PAL-->NTSC exist, these are more the exception than the rule. And even when they do convert it, the conversion is often less than stellar.
Out of interest's sake, I do know that the Panasonic players in China which come straight from the factory as all region, do not convert PAL-->NTSC, although some do convert NTSC-->PAL.