Firstly, thanks for the posting. Fantastic idea, being able to rate specific periods within a genre. Will definately look into that one.
Support for genre rating wihin the recommendations will appear in the next site update. You should then see the hip-hop and R&B artists/tracks disappear from the recommendations as you've rated the genres.
Something we are looking at is the whole area of genre classification, as pop/rock as a genre is quite broad, so you can get Pink and Punk in the same recommendation (some people may like that!). There are sub-genres which provide a tighter grouping of artists etc., and we are looking at the best way to expose these at the UI level.
Right now there is some support for defining preferences to certain period, although its only exposed at the item page level i.e. if you go to one of your country artist pages you'll see recomendations which can be steered towards modern day artists, or all time artists. This is one of a number of "biasing" algorithms we are trying out. This one basically boosts the probability that a newer artist will appear. Another model that exists (in code, not exposed on ite, yet) allows you to boost specific dates within the timeline e.g. if you like 70s punk, you can boost everything around 1977, making it more likely that something from that era will appear. This "era biasing" still experimental, but it's along the same lines as your genre/period suggestion, so i'll look at this one again to see how i can fit that in with the genre biasing code.