I have the same issue and it drives me bonkers.
In my case is the spanish music genre. I selected two pre-created "Merengue" station that itunes had available when I was setting up my iTunes Radio. I pay for iTunes Match, so I don't get commercials. yeah right!.
Not only do I get Spanish commercials, but over 50% of the songs are "Salsa" and not "Merengue". HUGE difference of genre and down right quite insulting. I understand if this was a wider genre like "Latin Hits", but the tittle of the stations as pre-selected by Apple are "Merengue latino 100% Radio" and "Dominicano Soy (translates to Dominican I am) - Top 40 Radio".
If I wanted to listen to "Salsa" music, I would create a station just for that, but I selected two "Merengue" stations because that's what I like. Both stations suck, and to throw salt to the injury, clicking on "Never Play this Song" doesn't have any effect on my selection. I always hear the same songs that are already in my list of never to play those songs again....
With the huge amount of "Merengue" music I purchase through iTunes, you would think the selection on their radio stations would be way better, but I'm baffled at how this is handled.
I would gladly go work for apple and separate the two genres where they belong. It's not hard, just listen to the drum beat, two totally different styles of music.
So I went back to pandora.
I'm happy.
The end.