In regards to Speck (my current favorite case manufacturer) I would assume Apple does know. The Candyshells for both iPhone 4 and the iPad were Apple exclusives (AT&T apparently counted as part of that deal too). The were only available upon initial release on the Apple site, at the Apple store, and the Black was available at AT&T retail locations. They didn't hit other places until a month later and even then they were in limited supply.
Also the Fitted was the first iPhone 4 case I saw in an Apple store besides Apple's own Bumper so I would assume with a few manufacturers there are relationships there for relaesing of products. There obviously is the basic one of distributing specs so the cases can be made in the first place.
Also the Pixel Skin HD is a great case but I prefer the Candyshell (yes, even with the scratching). I'm curious though, if there will be a redesign for a universal version or if there will be 2 seperate versions like in the case of the Fitted.