Rocked?

On the hit NBC show "30 Rock", most of the main characters are played by well-known actors. Occasionally, there are guest stars on the show like Jennifer Aniston, Matthew Broderick, Nathan Lane and Carrie Fisher. These guests play new characters, not themselves. They are never confused with their real life doppelgangers.

But at other times, the guest star celebrities play themselves: Whoopi Goldberg, Conan O'Brien, Oprah, and even Mayor Bloomberg. They are viewed by the characters on the show as their real-life selves.

This confuses me.

Why don't the characters who work at the very real 30 Rockefeller Center on "TGS with Tracy Jordan" know that they are competing with a very famous sketch show called "Saturday Night Live", which is taped in the same real building? 

Why do the characters recognize Jerry Seinfeld as Jerry Seinfeld when he shows up on the set, but they don't recognize Selma Hayek as Selma Hayek when she shows up?

How can Rachel Dratch (who was on SNL) play several different characters on 30 Rock, but no one on "TGS with Tracy Jordan" recognizes her as the character she played the week before or as "that funny dwarf-gal from SNL?" Nor do they recognize the actor playing Tracy Jordan as Tracy Morgan, whose name sounds an awful lot like the actor who was on SNL?

It's like in horror movies. After the buxom blonde takes a shower in a creepy hotel and hears a strange noise in the closet, she cautiously approaches it -- as if she's never seen a horror movie before. "No! Don't go into that closet! The killer is in there!"

Doesn't matter. Characters in TV shows and movies don't have TV's or watch movies.

And that's a little confusing.