One thing to consider is that the teams may not be totally ordered by "buzz". So everybody won't naturally gravitate towards the team with the most "buzz" because no team has the most "buzz"! There are also other factors: everyone has different preferences and teams are interesting not just based on what they do but on how they do it and on the people comprising them.

There is, of course, a decent amount of grunt work. However, a lot of programmers don't just enjoy programming as such but also enjoy making something cool. I know I'm certainly willing to spend time ironing out the bugs in my hobby projects because having something that works well is just as fun as writing something novel. Also, I suspect that everyone at Valve puts effort into minimizing the grunt work as much as possible, meaning they probably have far less really boring things to do than most other companies. So a bit of cleverness and forethought combined with a passion of creating something of quality can get good programmers to do the grunt work.