Question about pop music?

I am just curious. Do you think that pop singers today just sing, or do you think they actually understand some music theory? I studied it in high school but I am just curious if people like Katy Perry, Britney Spears, Miley Cyrus, Hilary Duff, Ke$ha and more actually have at least a basic idea of it. Do you think they do unedstand a little at the least or do they just rely on their studio musicians to write everything and autotune what they are doing? Any opinions? Thanks.