Often, when one says something in the format "A, but...", it has the effect of rhetorically negating A. It doesn't really matter what A is, it's what comes after the "but" that matters.
For example:
"I think you're a really great guy, but..."
"I'm not a bigot, but..."
"I'm really quite responsible, but..."
"I never wanted children, but..."
Three out of the last four Escape Pod episodes I've listened to (I have not been listening in order) have begun with an "A but..."* format about the episode's rating.
*I don't know if they literally used the word "but". But the sense was similar.
Things along the lines of:
"The episode is rated PG-13 for language, but if it were me in that situation, it would be rated R! (laugh)"
"This episode is rated R for [reason], but [humorous justification]"
This rhetorical negation has the effect of making it seem as though you don't really believe in or care about the episode ratings. It's as though you were embarrassed by them, or were providing them under duress.
If you're going to provide these ratings, don't it halfway or apologetically. Stand tall and do it right!
I for one appreciate the episode ratings that you provide. I hope you keep doing them. But I also don't like feeling as though you're rolling your eyes at those of us that appreciate them.
Thank you for your attention.