The music player of Pandora has undergone some changes, which van be read on their blog. Pandora has updated their playlist engine to play a greater variety of music on the personalized stations. They mention the following on the blog:
"For some time we've known that we weren't playing the full breadth of songs in the Music Genome Project collection. This was a problem with our approach to playlist generation; it really didn't have anything to do with the size of the collection itself. We've been hard at work on this, and tonight we're rolling out a significant upgrade to the playlist generator. Don't expect to notice a big change right away, in fact it might take a few hours of listening before you notice at all, but it's there. Your stations really will be playing all kinds of music that they wouldn't have before. Hope you enjoy the new music."
This is relevant information regarding my research, where variety is a major subject.