It is not IE only. CreateJS works well in the major browsers. The games work in new versions of all browsers. The games are only ad-free in IE and should work well especially in IE 10 as this looks to be partially sponsored by Microsoft.
Some of the links at the end also pertain specifically to IE.
I don't really know why they are pushing IE10 since it's not even out yet (unless someone is sponsoring them). By the way the small demos are working in chrome, quite slowly but working
I can only imagine they're slow because you don't have hardware acceleration working in your Chrome (type about:gpu into your address-bar to see what the deal is). All demos run smooth for me, as do all the games in the atari arcade: http://atari.com/arcade
I'm generally very impressed with what they've done here (aside from the 'install IE10 to remove adds' thing).