i'm one of those people leasing on a regular basis and i would assume that many of the people on the charts are also doing quite well.
On a side note, I don't want to make it seem like it's all about soundclick. Soundclick is simply just a hosting site that happens to have many artist looking beats, but you can't fully depend on just that. You have to go out of your way and promote all over the net to find artist and really make some decent money. It's really a lot of work.
There's a lot of producers on soundclick that have gotten major placements of that site, like johny and vybes. i know wacka flocka has gotten beats from soundclick and other artist like soulja boy, lupe fiasco ext... i've personally have been contacted by major labels through that site also.
Ok but what about this.....my friend just sold a beat to a local artist who is kinda buzzing for $1200....had he been a "soundclick producer" im pretty sure the rapper would have gone crazy if he found out that the same beat he paid $1200 for 9 other people bought for $15 each.