Aphrodite the html5 compatibility it is not an issue, no website no matter how was built, now is automatically working with html5 content also, since doesn't depend about their scripts or HTML code but the browser you are surfing, and most browsers this days are html5 compatible.
as an example i can build a website purely in flash but then embed a html5 game into it, it will work, as long as you do it manually, but im guessing most of the website owners they dont want to do the dirty work, so they just want to click and upload.
by not having a fast integration for the websites, the sentence above can make a bit sense, but then the meaning of the sentence is a totally brain fart, since it doesn't matter in what frame u build your game, but how you marketing it and how you can improve the spread ratio of the content!