Leaving aside the fact it'd be following the lead of a company it's turned into a metaphor for dinosaur business models, Netflix just isn't digging the idea of offering games. Said a company spokesman to The Consumerist:
Video games are a different economic model than movies and TV episodes, on which Netflix concentrates to provide the greatest convenience, selection and value to consumers ... Movies are perennial. A great movie from 1972 is still a great movie but who wants to play Madden '95?
I dunno. GameFly seems to be doing alright with it. But maybe that's because it's not offering Madden 95, and instead has a library of games people do want to play.
Blockbuster Considering Adding Games-By-Mail Service [The Consumerist]