No, I don't really see a lot of fic where authors are saying ahead of time "don't." Nor do I think silence should be considered as tacit permission. I just think it's pretty easy to ask for permission, and I'm not sure under what circumstances one wouldn't want to (a surprise gift maybe?). I mean, I haven't heard of any case where someone had zir fic recorded and and got mad about it, but that doesn't mean it couldn't happen. So, I think it's just easier to ask.

So, basically, I was thinking about a situation where one asked for permission, and was denied. You could go ahead and do it anyway, but why would you want to when there are so many people out there who would be fine with their fic being recorded?