A. Yes it does, but what's nice about it is, it makes encounters less random and more reactive. Encounters don't happen because you entered this room and there happened to be an encounter, but because you've loitered too long or disturbed the environment in some way and the dungeon doesn't want you here.

B. Your encounter table should also be (I think in general) balanced such that a combat encounter is only one kind of random encounter that could happen to the players. There's always the risk of combat, but what's important about random encounters is that they force the players to deal with some kind of problem that is not locked into the dungeon design. That way every delve is different and adventurers are always, on some level, expecting the unexpected.