These men are already in relationships, so we can assume they have the option of sex pretty regularly. So it makes sense. They're not desperate to have a bunch of sex. It's a stupid "study" in the first place - if they asked me, I couldn't give them a straight answer, cuz it'd depend on the day and moods and horniness levels and all that. Sex is a basic, primal "need", and it's (often) great. If you're starved for it, it's the ultimate activity. But not everyone's starved for it. It's like that tube of cookie dough I bought with my allowance when I was a little kid. It felt so damn awesome at the time, but now that I can buy a tube of cookie dough whenever, I'm not likely to do so very often. Well, OK, sex is better than a tube of cookie dough, but I think it's a (sorta) valid comparison.
What sucks most about all this is the surveyed blokes finding their "partner hard to please", and the suggestion that they should be spending more money on their ladies, blah blah blah modern relationships = prostitution? I hear this all the time - the distorted worldview that a guy will do anything for sex, and that he *should*, because what the hell, is he crazy? Modern culture tells us to take her to a movie, buy her dinner and flowers, go through all this shit that we supposedly don't want to do, to "earn" some holy-of-holies sex at the end of the night. Thank god I've never had one of those normal "dating" relationships. If my gal and I wanna have sex, it's cuz we both genuinely want to, and there's no currency changing hands. I don't see her as some awesome goddess at the gateway to sexual-bliss-land, who must be plied with roses and chocolate so I can earn my glorious rocks-off. Usually, I'd rather play video games, or play music, or read, or go out, or do some other activity that, believe it or not, can be more fun and interesting than sex. And she's the same way. And we still have sex, and it's good, nay, *better* because it's not placed on some stupid unrealistic pedestal.