There's another reason to do this, beyond Wolverine DVDs costing more than My Little Pony DVDs: inventory utilization. The demand curve for a new release goes something like this: BIG FREAKING SPIKE, two weeks pass, long-tail until the sequel is released. To accommodate peak demand, Netflix would have to do what Blockbuster does: order a metric truckload of Wolverine, then either let it suck up shelf space or dispose of it somehow after the spike was over. Alternatively, they could just not accommodate peak demand, and have users perpetually ticked off that they can "never watch anything I want to watch".
I use one of the Japanese analogs to Netflix and this is the #1 complaint everyone has with the service. You're lucky to be able to watch a new release within a month of them getting it, which sort of defeats the purpose now doesn't it. (Note that they offer plenty of UI features Netflix doesn't which tend to exacerbate this, such as "Sort by Popularity", "Sort by Release Date", and "Most Popular Recently Released Movies". They also have "Sort by Availability", which is essentially "Show me popular new releases from 2 months ago where you now practically can't give away the DVDs.")