I would assume you're right about that. The ones that continue to chase fame and do records and endorsements and all do probably very well.
One young lady I know, my kids former coach, has been on and off the show since the beginning (it was such a sweet show when it started) and she's doing a nice middle class income teaching and some exhibitions. No Mansions, no private planes, but what most of us would call a comfortable living. She's not really into the fame chasing thing though, despite being on the show I guess. I'm sure if she wanted more she could get and agent to track down things for her to do.