In the Critics Notebook blog, the writer, Ann Powers, posted this comment:
Pop is a wide open field. It really describes whatever is popular at the moment -- usually hybrid forms -- even Gaga's music is a mix of Euro dance and glammish rock via Elton John. Rock, on the other hand, developed an unfortunately stringent set of rules as it matured, and a very masculine stance. "Indie" rock has more room for different kinds of people, but mainstream rock remains pretty much a guys' game. Pop has big male stars -- Jason Mraz comes to mind -- but rock still lacks many major female artists.
Speaking of which, everybody needs to check out Heart's excellent new album, "Red Velvet Car"!