I'd bet it's not zero days, but one stop shopping. So the consumer saves the overhead of wondering, "wait, is this on Hulu? Netflix? Amazon? iPlayer?" The entire catalog is in one place.
I think Netflix and Amazon are getting to the point where their catalogs are deeper than usenet.
Of course, most film junkie's "essential 100" lists will still probably hit somewhere less than 10% representation on Netflix: http://blogs.indiewire.com/shadowandact/films-on-spike-lees-...
Still an availability problem though.