They can be made with whatever web technology the developers want to use. I believe however that Angry Birds is HTML5 though.

Yep, it's written in GWT. http://www.quora.com/Angry-Birds-game/How-did-Rovio-build-it...

I doubt it. I know non-game apps can/do use Flash. Remember, Google bundles Flash with Chrome.

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...