Bugs are prioritized by severity, meaning crash bugs first, then crit path quest bugs, then major quest bugs/gameplay bugs, then minor quest bugs and tuning. From the consumer's perspective, there's just a large mass of people working on bugs, but in reality, individual members either should not fix, or are not capable of fixing, any given bug that's in the list.
For example, a programming bug would not be assigned to a designer, and a design bug would not be assigned to an artist. Even within a discipline, certain people are suited to fixing certain bugs. I do all weapon tuning because I did almost all of the weapon implementation. Quest designers fix their own quest bugs because they have the most intimate familiarity with how the quest is structured.
Assigning a critical quest bug to any warm body who happens to be occupying a chair can result in a lot of inefficiency -- and often new bugs created by the attempt at a "fix". Similarly, there are idiosyncrasies to how some sections of game code work that really demand the attention of one or two programmers. Throwing new programmers at the problem would likely result in them spending twice as long orienting themselves and possibly making some poor engineering decisions.