Obviously there's a market for that sort of porn, otherwise there wouldn't be so much content, but I personally get skleeved out by watching it. I guess if you think about it, watching 1on 1 porn is still watching some other guy, so why is watching 2 other guys so different? But somehow we internalize the 1 guy is us.
OTOH, I can kinda sorta see the appeal of a 2x2. Might be a slightly more economical way of sampling two girls!
Related question, is it just me or is the dp and gangbang thing significantly more prevalent in Japanese porn than western porn? Release the cultural pontification hounds!