As far as I know, the message from root saying you got a reply stays in the top of your chatterbox nodelet until you manually delete it.
Yes, I know. But what I meant was that it's more of a one-time thing. After you delete that message - and who wants those hanging around? - there goes your only notifier. Plus it's still not a count, just a single notification. Different purpose.
Of course, one shouldn't expect replies to nodes other than thread-starters, ...
All I meant here was: Suppose you write a node that starts a new thread. If it gets no replies, that's interesting. But the if a reply does not itself have replies, that's not necessarily as interesting. The thread has to end someplace. :-) (we hope...)
So what I'm saying is, if the statistic existed, I would personally NOT consider it significant if a node I wrote had zero replies, if my node was a reply in the first place.
And yes, I agree that having the reply count for any node - not just the top node in a thread - is the most useful idea in all of this.