At this point, my guess is the majority of games are HTML5 based. Look at all the HTML5 games that came out of Mozilla's Game On contest for example. https://gaming.mozillalabs.com/games/

They can run in whatever technology the browser has installed, which can even include Java applets. Runescape for example. https://chrome.google.com/webstore/detail/ajjblpfpopipimofkh...