I'm a woman so I'll give my two cents.
As for the debate about who has the higher sex drive: without a doubt, a man. Of course there are always exceptions to this rule, I know alot of women who have insanely high sex drives. But overall, its men who want it more and enjoy it more. Its called testosterone. You guys have a steady stream of it and we don't. We're stuck with a mess of up and down estrogen that gets fucked with if we're on the BC pill. But I'll guarantee one thing and guys listen up: If you rock in bed...and give her the best sex she's ever had....then she'll want it more and her sex drive will skyrocket. I think most women tend to not enjoy sex or want it because they're bored, or their partner doesn't know a thing about her hotspots. Every woman is different so give her a custom made sex session just for her and she'll want it all the time.
And as for sex declining during marriage....doesn't always happen. I think if it does, then either see above, or understand that eventually children come into play, responsibilities are added, thus stress is added...you get older, women hit pre and post menopause...all of those might attribute to the frequency of sex because they all affect our libido. Its been proven that if men picked up more chores, bathed the kids, paid the bills etc...just took some of the workload off their spouses, then they'd feel more appreciated and be more inclined to make love. Help her out and she'll help you out too hehe.
But yeah...I'm pretty satisfied with my partner. We've been together three years, are married now...sex doesn't happen as often as I'd like, maybe once or twice a week, but our schedules conflict with each other so we don't get the time each day to even sit down for dinner together, let alone make love. But when the opportunity arises, he definitely curls my toes.