I think if you ask, women will try to flatter your dick no matter what. Girls KNOW that in our society, people make a big deal about a big dick--So if she likes you, why wouldn't she flatter you about it? Also, I've read too many threads here about hung guys who've had girls say things like "It's big, but I've had bigger" or "I like how thick it is, but it'd be better longer", etc. Lots of the girls that said that had issues with the guy before, or the guy asked it in a very cocky way--"So, is this the biggest you've ever had?", "What do you think about my size?" etc.
I'm 6 1/2" and my ex girlfriend, tried flattering me. She asked me how long it was and I told her the truth, then she concluded on her own that it was a "nice size". Did she really think that? Maybe, maybe not. She certainly always wanted to have sex with me and almost always initiated it, even while we were broken up/on breaks/In huge fights/etc. We had public sex all over the place. I've fucked her sore. Does this mean that she was actually 100% satisfied with my dick size? No, she just liked me, liked having sex with me and knew that I'd be flattered if she complimented my size. Out of all the girls I've gotten with, only a couple said something to flatter me in that department. The rest didn't say anything. I never expect them to. Most kept calling back though, so they obviously were not totally disappointed by my size.
But anyways, think about these typical guy/girl question/answers:
"Is my (5 inch penis) too small?": "No, it's not small. It fits perfectly"
"Is it weird that I have a curve?": "No, it hit's my g-spot. It's perfect"
"Is my dick too big for you?": "No, it hurts but I like the pain. It's perfect!"
No matter what, girls (who like you) will always try to flatter you, even if it's not 100% true. That doesn't mean she pitties you, or isn't actually satisfied with you, she just wants to make you feel best about yourself because she likes you! Same how a girl who doesn't like you will try to downplay you, she knows how much it'll hurt your ego.
But yeah, speaking on just "does size matter", the "yes" version of the answer is always an extremely broad one. It really depends on how you view the question. When girls answer, many have a very different view on it.
One girl may have been with three average guys and one small guy. She had good experiences for the most part with the average guys and a bad experience with the small guy. She would say size matters.
Another girl may have been with three average guys and one big guy. She might of had decent experiences with the average guys but an amazing experience with the big guy. She's going to say size matters.
Then there are girls who have had all ranges and say that average fits them best. Or a small guy made them achieve orgasm when a big guy didn't. Or a big guy hurt her and didn't know what he was doing. Etc, etc, etc. They'll tell you size doesn't matter.
That's basically it in a complex nutshell.