Via MacRumors:

Apple’s interest in SproutCore is, in part, to reduce their dependence on Adobe’s Flash player, which traditionally is used for more interactive content on the web. Being based entirely in JavaScript, any modern web browser can run these SproutCore based applications without any additional plugins.

Despite it’s common usefulness right now, Flash is ultimately a closed, non-standard blight upon the web and needs to open up or (preferably) disappear.

See also what is essentially Keynote for the web written in a Javascript with their own Objective-J framework, from two former Apple employees.

Squirrelfish is making a lot more sense now.