@JasonR,
Firstly "thrive" is a very relative word, in the same way that the term "Face Clawing Misery" was used by me exclusively when forced to watch 'FRIENDS' on TV by 'friends' in college. But I am very sure many here would differ on that.
The point I am making is that context matters a lot when you use certain words. The book goes on to establish the context of the people and their lives, right in the beginning, before going on to recount their daily routines. I assure you, all of them in the book "thrive" from their "relative" positions within the "World" that they inhabit.
The title is *not* a misnomer as you have been constantly bringing up. So far, I have been answering to the "sense" of your questions so far, in order for you to grasp the modality of the situations that look so far-fetched (to most of you). But I have to highlight these above points to you now.
That does not mean they are 'well-off', but they are making the most of their situation in a better manner than our own imaginations allow us to see. They are also making the most of their situation in a way better than the "bourgeoisie" are doing with their own situations.
ETA: JOSH's reply above very much captures what am saying, that too, with LA being the "context".