Sometimes I'm in a very specific mood and try to keep a variety of stations for that reason. For instance I don't want Korn to play on a Hair Metal station. But I still want those songs on the appropriate station. Or I don't want journey playing on a station geared towards strictly Chick Rock. But I want to keep listening to journey on their station. You feel me?
Accoridng to this question on Quora, downvotes are station specific.
Thumbs-up/thumbs-down are station specific because otherwise if you downvoted a Katy Perry song on your Classic Rock station then it would affect your Katy Perry station too. You use the thumbs up/down system to individually craft each station to your preferences.