U of Md. College Park published all employee salaries every year. I always was entertained looking up bad profs. and seeing how much (or little) they made.
The motivation is the same as one gets from moving from C to C++; you start with a small language (in this case, assembly) and then build on top of it. I've tried this recently in my own course, and found that the morale boost from having something that actually ran and produced results that they understand significantly improved learning.
As for AST design, it is easier to design the AST first than you might think. Just ask the designers of Lisp.
The music site Magnatune (http://magnatune.com) does that.
They split your money into two piles, one for downloading (you can download anything you want) and one for streaming.
While I don't know exactly how magnatune works, what you've described is completely different from what I've said, unless your streaming pile is distributed only among artists you streamed, and not put together with everyone else's money and distributed among all artists.
Having just superficially perused Magnatune's info pages, I couldn't find anything specifying how they determine the amount given to artists, other than 50% of it goes to artists, and the other 50% goes to Magnatune...
