As the OP said, as long as they abide by the rules, they can post as infrequently as they like. Have to be honest, though; it pisses me off when you see someone that's been a member for 6 or 7 years, and the only time they seem to post is when we lose. Where were these "fans" when we were picking up trophies for fun in the intervening period? It comes across, rightly or wrongly, that they're on here waiting for us to fuck up. And the time argument doesn't really stack up, for me anyway. How long would it take to make, say, half a dozen posts in a day? Should it annoy me as much as it does? Undoubtedly, no. But, at the end of the day, it's their choice.
I guess I'll need to book an extra session or five with my counseller.