It's not really about Grove vs HipChat but more IRC vs HipChat. IRC is a really old and open protocol, meaning that hackers built lots of tool around it and already love it. But it's a pain to configure and maintain it if you've got more important things to do. (Like building your app). A couple years ago, I believe grove wouldn't have stand a chance against the hacker mentality of "I'll do it myself", but now that more and more companies need to go as fast as possible, it makes sense to pay a little bit to have a service that's stable and just work out of the box.

And, for me personally, I hate HipChat clients (IIRC they run on a crap adobe version?) and I like using the existing tools I have for IRC. For instance, I've already setup everything to work on my vps with irssi, with the plugins I want, the theme I want, etc. I don't want a "new and prettier" solution to a solved problem.

Because native clients are significantly better than non-native clients, and Adobe Air apps are the worst.