ufc 48, 50, and 51 had non-title headliners ahead of championship fights. doesnt make it right, but it has happened. mir-sylvia at 48, hughes-gsp at 50, and tanner/terrell with arlovski-sylvia 1 at ufc 51.
those 4 fights had more hype than rousey/carmouche and mightymouse/dodson. the ufc had few names back then, so they relied on ken shamrock and tito ortiz and needed those names on the poster. henderson and machida are not the biggest names, but they are both pretty big by now.
rousey, despite her perfect and unique record and her appearances in the mainstream, is not a name. they will need to heavily highlight the undercard during ads. this is one case in which the main event couldve been a non-title bout. hopefully the ufc's marketing of ronda and women will also succeed, but i'll be the first asshole to log on to my petty little account on our petty little forum and say "told ya so"