Adobe still has its clutches on flash, and its premiere which refuse to support it officially, same with apple. But lets take a look at what does support it. Wow, only apple and IE, fancy that.
Adding to the fact imgur and 'gfycat' try and fence sit by creating a wrapper and container both an mp4 and webm file with the latter offering a baseline profile on their h.264 inside the mp4 for wider support and imgur shitting the bed.
The multiple amounts of profiles available for h.264 might create better quality/size comparisons on benchmarks with vp8 but does the codec a disservice when trying to become a standard. Plus, its still licensed code.