The song blew up crazy because of the following:
Kanye co sign. Def Jam's relationship with top DJs. The ability to push the record to the entire market / service it to *all* radio stations. Placement through various media sources. Well placed tweets from taste makers referencing the song. Using connections to get writers at sports shows to pen jokes including the song.
For all you guys who want rappers to forever to be independent, to keep it pure, and to hustle out of their trunk talking shyt on major labels.....this is what they do. If they get the right record and by the luck of the music gods a song gets mildly popular they can take it to the next level.