This isn't about patents, it's about one simple thing: GPUs aren't actually suitable for video decoding. A lot of effort required for not much gain.
Yeah, I've been preaching this for YEARS, but most people apparently still like to believe in fairies. Shader-based video decoding is simply useless for the vast majority of configurations. You can't offload some of the most demanding parts of the pipeline, it's WAY more power-guzzling than CPU decoding, and you need a somewhat beefy GPU to start with.
But it's still good to have VDPAU, as it provides a very capable presentation layer, much better than the old Xvideo.