no, they can do it. There is overlay support in current generation iptv support that can target scrolls and texture replacements at a resolution of less than a zipcode. Take that gear and apply a few static watermarks with timecodes and then swap the different streams at unique times for each viewer and you can end up with a stream thats uniquely identifiable.

Motorola's (Google) new gear can do this, though the purpose is targeted advertising not watermarks. The truth is streaming DRM is about preventing your mother from giving a copy to the neighbors, almost all the content is already on P2P by the time it streams.