The music in The Sims 3 70s, 80s, & 90s Stuff has been explained in a new blog post on TheSims3.com:
The Rap station features slammin’ songs from The Sims House Party Expansion Pack, another nostalgic nod to the original The Sims. All the musical talent are from the Oakland, CA area – free styling to the beats created by our very own audio team!
> “The Sims 3 70s, 80s, 90s Stuff is Now Available!” at TheSims3.com