Of course it is, and you can post the same length post of the same quality anywhere on the boards (so long as it meets the minimum characters...)
Why should a rubbish post on one part of the boards be worth less than an equally rubbish post on another? Same goes for good posts, mediocre, and any other quality you can think of.
If something meant to show the amount of posts you have doesn't show the amount of posts you have, then it's useless by its own definition.
This is one of the best posts I've seen regarding post count, I agree completely.
Post count in off-topic does seem to make people post more uselessly there, but at the same time, it has the same affect towards the PnP sections when it is inactive in OT. I'd personally prefer the OT section to be flooded, rather than the other way around.
Hell, it would be even nicer to remove post count completely. But, I suppose you could then argue that we should also remove avatars, sigs and names, along with illegalising any displays of personality.