It seems we've heard this one before. Jay Leno is retiring and being replaced with a younger, hipper "Tonight Show" host. You might remember back in 2009 NBC "retired" Leno from the iconic late night show and replaced him with Conan O' Brien, a move that failed miserably and led to Jay reclaiming "Tonight" less than a year later. This time, according to multiple sources, the replacement would be Jimmy Fallon. Why the change?