I didn't read every post so someone may have chimed in on this (cuz it's pretty obvious). The rock stars with the most money are the ones who WROTE hits, not just performed them. WRITING and OWNING songs is where the money is. So it matters lees how many albums different artists sold (although is does matter, just not as much) but whether or not you own it. If you own it, you get payed every time it plays on the radio, someone covers it, it's used in a movie, it's on a "Best of the 80s" CD of some other collection, and every single copy that sells be it a CD or iTunes. The same goes for all genres. I bet Brad Paisley is worth a lot more than some other famous country singers because he writes (at least part of) a lot of his songs.
Plus, as some already said, it's all about how you MANAGE your money. If you made it and blew it you don't have any more. If you made it and saved it, your net worth is still high (again pretty obvious).