I always ask this question... Why does people expect Pop artists to sell a lot of albums? I could explain why, but I'm too lazy right now
I mean, the only one "pure" Pop artist that can do it is Britney. Gaga is yet to prove herself.
I think that a lot of exposure is what helps sell albums. I mean, look at Rihanna. She wasn't known internationally or that popular before GGGB. Her popularity skyrocketed with that album and that helped her sell albums (Ofcourse, also good single choices, promotion... Although I think DJ didn't use all of its potential).