Oh, forgot The Fame Monster was up that year. Teenage Dream must've scraped into that category by the skin of its teeth. It must've had the pure pop voters whereas The Fame Monsters had Pop and Dance voters, each genre pretty much had its own entry that year so maybe the 5th slot had a low entry requirement. Dunno, I'm basing my assumptions on observations not insider knowledge.
I don't call them Pop voters meaning they *only* vote pop acts in every single category, just that they come from Pop fields in the music industry. Beyonce and Katy are both female pop stars that pop fans love, their votes will have definitely been split and Katy doesn't have a secondary voting block to support her (plus Ed and Pharrell stealing votes, very pop friendly category this year).