Question for Blockbuster

A frustration with my Blockbuster "All Access" subscription triggers this question...

How come Blockbuster will rent "unrated" versions of slasher crap, gross-outs like "Jackass", and bloodier battle scenes and not legitimate "art house" movies like "Lust, Caution", "Henry & June", and "The Cook, The Thief, his Wife, and Her Lover" that happen to have been slapped with NC-17 ratings? (They do offer an R-rated version of "Lust, Caution" - the one that was made for the mainland China market - but not the version that fully reflects the director's vision.)

I can accept not putting them on shelves in stores where insufficiently parented children might pick them up, but since the online service relies on a credit card to access, there's no reason adults shouldn't have access to them.

It's not like the policy is just a simple, straightforward "no NC-17" since they list "Last Tango in Paris" and John Waters' "A Dirty Shame" in their offerings.