Isn't turntable.fm a video game? Most video games have a fad cycle. Game developers realise this and cash in on their hits immediately. The 'gain users first and patiently monetise' strategy has no place in the world of gaming.
I've never used turntable, thought it was dumb, but did it ever make $? Did they ever even have a plan to make $? Seemed like a giant fad to me and can't believe they raised $ successfully - especially with having to deal with music licensing.