Browsers other than Chrome also support HTML 5. Sure, support is partial at this point, but the standard hasn't even been released yet. What makes you think someone would develop an app that only works on Chrome?
Projects like Google Native Client ( http://code.google.com/p/nativeclient/ ) makes me think that. If you can execute X86 code and leverage hardware acceleration through a browser that would probably be worth telling people to download Chrome to use your app.
