The problem -- as I see it -- with the whole "does size matter" issue is the way it's presented in society and the media. It's often shown as "bigger is always better" and despite what TV shows and college-themed movies would have us believe, that's not necessarily true. What I believe
most women mean when they might say "size matters" is not that "bigger is better" but, instead they'd like a size that is compatible with them.
If you think about it, that makes sense. First of all, how many women
really want to be poked and prodded by a 12" shaft of flesh? Maybe they'd be interested in
looking at it, but I doubt very many would actually want it probing their insides. Even if a woman did want that, it wouldn't matter if she couldn't effectively and comfortably accomodate it. Not all women can, despite what porn may "teach" us. What good is sexual intercourse if it hurts everytime?
So I think all most women mean when they say "size matters" is they'd like a size that is relatively compatible with them -- not necessarily something that resembles King Kong's schlong (or possibly Eric). Besides, I have to imagine that the man attached to the penis is more important than the penis itself. After all, if women only wanted the penis (and not the man), it'd probably be a lot less of a hassle to just go buy a dildo or a large vibrator.
NOTE: This is just a theory thought up by a man, but based off discussions with numerous women of different ages and relationship status. This theory may or may not work for you; if it does, great and if it doesn't, that's fine too.