That is actually pretty terrible advice for a lot of people. Not everyone can/wants to separate sex from intimacy and that can lead to quite a few problems as well.
http://en.wikipedia.org/wiki/Evidence_under_Bayes_theorem
It could be that none of his bad situation is the result of his preferences, but his situation shouldn't be ignored either. You have to be able to consider that you did something unwise in order to take hints from the environment.
Conversely, the logical extension is that you should be on board with your partners freely having fun sex, with whomever they desire.
For example, I was recently in a situation where I felt no sex drive whatsoever, but greatly valued the intimacy of the particular relationship that was developing. The lack of sex drive had little to do with the partner's attractiveness, it just wasn't there. I have that sometimes.
Since for me 'sex was irrelevant', but for her sex and intimacy (understandably) went together, we talked about this and found a happy middle ground where we could share intimacy, and I could 'give her' sexual satisfaction without caring too much for it myself. In fact, I could do this precisely because I didn't care too much, and I was absolutely willing to do her a 'favor' (and it wasn't entirely unenjoyable to me, of course).
At some point she wanted a bit more mutual sexual desire, so our arrangement changed. Because we talked about it, this went quite smoothly and to this day there is a lot of intimacy (within the bounds of what is situationally desirable). I don't think we'd have gotten to that point if we had not had a whole bunch of good conversations about the exact relationship between sex and intimacy in the context of our 'partnership'.