I don't think Google has affected anything with this move. By any counts out there, Firefox has double the market share of Chrome. It might reduce the use of HTML5 video versus Flash video in Chrome itself, but for the whole web, it doesn't make a difference when Firefox already took this position with twice the market share.
I would argue that none of the desktop browsers are having an effect in this area. The only thing that is really driving the adoption of html5 <video> is mobile devices and their poor or nonexistent support for flash.
Many sites that serve mobile devices html5 video still serve flash to html5 capable desktop browsers.
Mobile devices will support WebM; simply because desktops/laptops still rule and there's tremendous pressure to support desktop technologies for content-delivery that are popular.
And I would argue that the majority of traffic for websites like YouTube comes from desktops / laptops.
This move might signify changes to be made on YouTube later, which will be significant for a large segment of Internet users.
Also, Chrome is heavily used by early adopters and tech crowds, so it will influence their perception of things and this might trickle down to more average users over time.
I for one, though do not use Chrome (I use Safari) myself, have put Chrome on every PC I help set up, until yesterday. Sorry, Google. I just like the fact that I can put up videos I shot with my camera on my website without transcoding and my friends would view them just fine from their browsers and phones. I don't know which side is more open - and therefore more right - in this controversy, but in addition to openness, I support industrial collaboration. And more importantly, video codecs are used beyond just web. How about looking further and see the frustration that the non-web video people would have because of this action.
