There are other sexual favors that can be performed that can more than make up for this, however.
I mean, if I wanted to go down on a girl, but she wanted to do nothing for me, I would not be happy. But if she doesn't want to give head because she doesn't like it in general, but is willing to do something else that would be considered special to make up for it, I would be cool. I don't even like blowjobs that much, anyways. A masterful handjob with copious lube feels much better.
Still, a woman who doesn't give blowjobs or a man who doesn't go down has to work that much harder to make up for the fact that they do not participate in this activity.
I just don't think oral pleasure necessarily has to be reciprocated by oral pleasure. But attention must be reciprocated by attention.