It's all about the perception of achievability. Like AJ Lee is a person you could just about imagine you might be able to nab if you show her your limited edition copy of World of Warcraft or some super rare comic book; whereas you'd have simply no chance with Trish Stratus and you know know it.(not YOU, just the expression) So, because Aubrey Plaza and Tina Fey don't have a million forums, websites and threads frequented by dedicated 'net virgins - as opposed to say, Megan Fox or Sophia Vergara - then one can convince oneself that because the race has far, far less participants, one might be in with a shot.
It's also very easy to have your opinion swayed by the type of roles people play. Vergara is hardly going to get offered the role of a comic book nerd, or a gaming diva, or a bookworm - is she? She's selling what she's got on the best platform available to her. And lets not forget these people are playing characters - they could be the complete opposite in the real world.