I'm sure that nearly all women who have tried a big cock (i.e. at least 7 inches) will say that it feels better than an average-sized cock.
I've heard a lof of women say that size doesn't matter right until they tried a big cock and then they suddenly became size queens.
Most women talk about cock size so even if those women who haven't tried a big one, will still know that a big cock is better. Women are brainwashed to believe that bigger is better. Just look at porn, Sex and The City, women's magazines, the media and the society in general.
I don't know how old you are but if you're young like me, then you will know that most young women today are size queens. Today it's damn near impossible to find a female under 30 - and especially under 25 - who isn't a size queen.
Most vibrators/dildos are bigger than the average guy so of course a woman is going to feel disappointed (at first) if the guys whips out an average-sized penis or smaller than that.
Sure, an average-sized penis might feel good to a woman but a bigger one is going to feel a lot better. That's why it's like being Sisyphus if you have a small or average-sized penis.
Who wants to have sex with a woman when you know that no matter what you do, it will never be good enough, simply because you're lacking those extra inches? Those extra inches that will give her the stretch that she needs and hit those spots in order for her to get fantastic orgasms.
(Come to think of it; women have it so good damn easy when it comes to sex. Men basically do all the work in bed and women don't have to worry whether their body parts are big enough for him to enjoy and get an orgasm from. They can just lay back and relax.)