Here's what David Hoatson from Lynx has to say about that:
"Hardware manufacturers must sign a 'contract' that says it is impossible to steal content using their device and driver. This puts all the legal burden on the hardware manufacturer if someone uses the device to steal content. Having to sign a contract to allow Sony to sue you for the acts of a rogue user doesn't seem appealing."
And some interfaces (as mentioned earlier in the article) cannot in any case meet those contract requirements without redesign.
Paul