Opera supports html5 on YT. Just disable flash and you'll see.
some videos not working if you don't use flash.
That's exactly the reason why I don't like to use the ''Flash Plug-in Trick''. And besides that, in some videos, the resolution is only available in 360p; The loading speed of the videos is less than in Chrome; etc. That's why I said: ''FULL support'', not only partial support.
YouTube could serve it to Opera if they wanted
So, The reason why Opera has this problem is because YouTube didn't want to cooperate?
H.264 is indeed coming to Opera.
I Hope this can solve part, or the whole problem.