VC is automatically added to meetings, every room is equipped with the proper AV, and culturally, people often actually click the right buttons to start the VC even when they aren't expecting VC guests. I don't remember ever attempting to join a meeting over VC and having the main location forget to join (although it probably happened to someone every once in a while).
At least on our team, we tended not to have those 2 minute conversations. The code-review tools are top tier, so we would use those if at all possible. Most of our non-meeting communication otherwise was in buganizer (the bug tracker), Google groups via email, Google docs, or IRC (they were getting rid of it around when I left).
I think the only exception was Nooglers. We had Nooglers sit next to a mentor on the team, and they would usually ask lots of simple questions out loud throughout the day.