.. though in all fairness it's often not about storytelling or humour as about picking up in a scene which character is the less likely to know the pop reference so another can jump in and provide exposition for those in the audience that don't get the reference.

The brain guy/gal knows about the science, fine arts and the more complex intellectual theories, but when it's pop culture he's the one who buys it even though it's often a stretch that he wouldn't know that (can't have genius know everything, viewers develop antipathy for the character - once in a while they need to know something he is clueless about).

They don't have much choice to do this anymore whenever the references aren't painfully obvious. If they don't explain, too many viewers will get up and use the next commercial break to look it up on wikipedia, and the media people at advertising agencies complain (they don't like situations in shows, especially before breaks, that "call" the viewer to his computer or to leave his sofa - and as they don't like that, the networks don't either.)