I know it's TV, but they're the exact same show!
Both shows have shows within the show.
Now check out the cast-
Mary, from MTM, is a single woman in her 30's who works for a TV show. So is Liz.
Lou, from MTM, is a man. Lou is the boss. So is Jack.
Ted, from MTM, is a man. Ted is stupid. Ted is the star of the show within the show. So is Tracy.
Jenna, from 30 Rock, is Liz's best friend. Jenna is obnoxious. Jenna is like unto Rhoda, Mary's best friend, and Phyllis, Mary's obnoxious friend.
Murray, from MTM, is balding. Murray has a wife. Murray also works for the show and shares the same hard times his female counterpart has, just like Pete.
I think 30 Rock is aware of the similarities. What else would explain the opening credits in the pilot episode? It's very Mary Tyler Moore-esk, but the song is ironic because it's not about the Mary character, Liz, but about Jenna... in a fat suit.
Apparently Stephanie told me this a year ago. It's so true!