http://www.youtube.com/watch?v=LphiRFvd40I - go to 6:49

Now one of the things with HTML5 is offline storage, it would be highly surprising if the N9 doesn't support this, so basically you can get an app by visiting a page, it has functionality provided by the various components of HTML5, if you like it, you save it as an app. If it's something like a word processor, it can still work even if not connected to the net.

This makes for a very easy development platform, and HTML5 is really the future, almost any device will support it, so it makes for an even better platform than any of the other ecosystems. Windows 8 is going that way too.