Youtube have never used any On2 VPx codec to my knowledge, but Adobe Flash and basically every video site on the web used them up until about 2 years ago when they started to transition to H.264 (though many still use it for certain bitrates) so your basic point remains that lots of companies, big and small, used or are using it right now without any patent problems.

(I assume Flash on mobile phones means they'll now all be exposed to the exact same patent risk too)