Keep in mind WebM is only a decade old, it takes time to support a patent-free video format that has readily available implementations, including BSD-licensed software ones. I'm sure Apple will support WebM when they find some money and finally manage to bring iPhones out of beta. Not every small phone producer making it is as big as Debian.
Anyway, if the default browser does not support something it should be easy to install an alternative browser, dumb phones from fifteen years ago had this ability (remember Opera Mobile?) and I hear iPhones are a bit more advanced so I'd expect them to let you do that. What kind of web-capable half-modern device wouldn't anyway.
Apple is holding back on WebM support arguably because it has interests in forcing people to keep using patent-encumbered codecs from the MPEG-LA. They did nothing for pushing an open video format for the web, quite the contrary. They are still fighting against this. Apple is the one deserving to be pointed the finger at. Let's not divert the blame here. I hate Google but we should recognize the rare good things they occasionally do.