2 years ago, while working at a SoC vendor, they were explicitely taking into account WebM support for their next generations of chips: not having hardware decoding for a major web codec would be a great failure: with Google + Mozilla + Opera we could see almost 1 billion users affected by this. This is a make or break to have design wins.
A SoC lifecycle can take 5 years to materialize in customer shipping hardware. Yet Mozilla is giving up before collecting the fruit of their previous policy (no system codec).
What good is WebM support in the SoC, or what effect does it have, if there is zero content out there using it anyway? If WebM video would be popular by any measure, this wouldn't have happened.
Note that there are SoC already out there that support VP8/WebM. As far as I know Tegra 2 is one of them. What does it change? Nothing. All those chips support H264 as well. So H264 is what content producers use.