A conspiracy theory for you to mull over:

Apple takes great care to ensure a long battery life for their iOS devices, by carefully controlling the hardware & software metaphors that impact it. The result is that iOS devices vastly outlast Android comparables.

By pushing the web towards the WebM codec, Google can very quickly knock a key benefit of the iPhone, namely H.264 hardware decoding, out of the equation. It seems very unlikely Apple will quickly pivot to add hardware WebM support, both because they are likely stubborn, and because of device constraints & their need to continue to support H.264. 

Thanks Google! I look forward to hating mobile video on my iPhone as much as folks on Android hate it.