I agree, the bigger isn't necessarily better. I was actually having this conversation with my boyfriend after he joked about wanting to add an extra 2 inches. I told him he was absolutely crazy for thinking it'd make the sex better, if anything it'd just be painful! I mean, sure it may be easier for a man of substanial length to "please" a woman in the most banale of ways, but sex is all about experimentation, fun, getting to know one another on a different level, and sometimes even love (of course negating having sex for the purpose of conception). Having an avg penis would probably boost a mans confidence and thus make him more apt to shake things up in bed due to the stigma around length, but there is nothing a man with a 10" penis can do that a man with a 8" or 6" or even in most cases 4-5" man can't!
I think a little insecurity about penis size adds a bit to the creativity of sex. If a man feels he lacks in the instant "wow you're penis is huge" satisfaction he thinks a woman gets (since men are very visual I assume they think we get satisfaction from that) he'll make up for it in skill since he'd have to work at it just a little bit more.
Ultimately if my man, whom I love dearly had a 2" penis, tho the sex may not be physically amazing or astronomical, i'd still love him, and i'm sure he'd be able to find other ways to please me sexually so no big deal!