The people in a company doing QA are different from volunteer beta testers. I thought most volunteer beta testers who don't work for the game company or are part of a testing service - I thought they played for free.
It seems to me that there are several kinds of beta tests. There's the beta test where you are testing an incomplete version of the game. There's also something called a beta test that seems more like getting into a game that's getting ready to be released - a preview or load testing. Aion seems like that. The betas for Aion feel like you are getting a preview of a game that is mostly done.
I was a volunteer beta tester for an online game that failed (several times actually, two publishers) - Uru. I was one of the first 100 to be let into the second beta test - the first test with outside players was very small, and started early in the development process - more an alpha test. in the Uru beta I was in, we tested incomplete versions of the game, but versions that had the basic game functionality. We logged bugs and we talked about what was working for us, not working, all that.
People sometimes talked about how much work it is was, also the work in being a volunteer forum moderator - I was that too, for several years. But you know, those volunteer experiences were fun, seeing the game before release and feeling like you were a part of something. People varied in how much they logged on, how or if they tested, and how many bugs they logged. I think it has to be fun - it's a volunteer thing. When you depend on volunteers, you can't make people do what they don't want to do.