Well, based on the numbers, they buy more movies than their PS3 counterparts.
The numbers I could find.
Standalone BluRay: ~650,000
Standalone HD-DVD: ~480,000
360 add-on: ~270,000.
Given the approx 2:1 ratio of S/W sales for BD vs HD-DVD, it can only mean that the BD owners are buying a lot less movies per player and/or the number of PS3s that are seriously being used as players is relatively small.
Or perhaps the overwhelming studio support for BD isn't all it's cracked up to be?