I guess there might also be some technical reasons why modern games don't (headshots aside) exploit location based damage a lot more. I'd imagine it could cause some problems with clientside prediction, e.g. due to internet lag it would be hard for your client to know the exact location you hit until updated by the server.
I seem to remember that even SiN, a 1998 game utilised location-specific damage, and yet it seems to have fallen by the wayside in modern FPS.
The gore argument doesn't necessarily wash with me, since games like Painkiller are just as brutal in terms of claret splattered floors and limbs bouncing off walls. I think the main problem people had with SoF2 was more a question of it depicting violence against humans, which doesn't seem to go down too well in some circles. Rumour has it, one of the reasons Halflife 2 features masked "combine" rather than more humanoid features is in order to get a lower classification.
^I'm not overly convinced by what I've just written since location-based damage on non-human characters isn't really that interesting to most of anyway, since it's hard to relate to. Blowing someone's leg off is a lot more appealling that blowing a tentacle off some creature or whatevre.