Link to Atari Arcade site http://atari.com/
Saw the story at Paul Thurrott's blog http://www.winsupersite.com/blog/supersite-blog-39/windows8/microsoft-teams-atari-bring-arcade-classics-web-144142 snippet:
"While the games at Atari Arcade can be played for free in any browser, you can play ad-free in Internet Explorer. And if you’re using Windows 8 with a touch-based PC or device, the games have been specially designed to support multi-touch."
Android & iOS are supported in addition to computers.
My girlfriend is testing Centipede on her iPad 2 as I type this ^_^ she hates Spiders, so she loves any game that lets her kill Spiders.
She is playing for free in Safari, they are also selling the games as Apps for $0.99 per game, at least for iOS.