Read the men and porn thread - and in fact any other thread here mentioning porn and you'll see that certainly most of the women here enjoy porn, either solo or with their lovers.
The reason girls / women don't talk about it as much as men is more to do with cultural norms and expectations (and the fact that there is only so much time in a conversation and the REALLY important things, like shoes, need to be discussed at length first - shoes and where did you get the top and yadayada). But mainly it's that women's sexually is not as openly accepted as men's still. Of course men like to look at pictures / movies of people fucking and such - but women? No they wouldn't like that kind of thing - give her knitting pattern and a recipe for something with chocolate in it.
And then there is the whole argument that women as more emotionally stimulated than visually - we'd allegedly rather read about Mr.Darcy making Ms.Eyre's cheeks rosey on a vigorous walk!
Well, FUCK THAT! - that's a load of shit - women are just as visual as men - I certainly am. I've been reading stolen Playboys and the like since I was 11 too. I've been watching porn since I had access to a VCR and older men and, I should hope it goes without saying, I've been using as a masturbation aid. And I'm by no means the only one.
So no, why the girls you've known haven't admitted it I should imagine they have all done it and if there are a few that haven't it is cos they've felt too repressed to go out there and get porn.