Personally, I feel that questions asking about VOIP services, on their own, are off-topic. Using these services has nothing to do with gaming. The first question linked looks to be on-topic, though, as there is a very real issue being encountered with a game.
We are, first and foremost, gamers. Our expertise may spill into other related fields, but at our core, we just like to play games. I think the questions about TeamSpeak, Ventrilo, Mumble, and all the other VOIP applications currently fall into a gray area. On the one hand, the programs themselves aren't about gaming. On the other, gamers use them lots for group activities. Arguments can be made both ways.
Obviously, we should be using our judgement when a question is asked to determine if it's on or off-topic. There are areas that can be borderline, but I think a baseline can be drawn.
A question asking about the functionality of ANY VOIP application, when not related to it's interaction with a game, should be off-topic. These are just generic programs, of which there are a lot. There's no way we can be experts in how they all function, or how to optimize them for best use. We're not VOIP.SE.
A question that presents a problem with a VOIP application, when in relation to a game, is on-topic. It has to be a specific game, though. Chances of someone running into the same issue, and being able to solve it, leverages our specific expertise much better than just poking a VOIP application.
So, to summarize:
Question about TS, Vent, Mumble, whatever VOIP program you use = bad.
Question about TS, Vent, Mumble, etc. doing something funky when playing Game X = good.