This also means interop will be easy, and makes it possible to have new blogging tools that are compatible with WordPress in new interesting ways.
May not mean much to end-users. By the time developers deliver features based on this stuff it'll be baked into the platform ten levels below the user interface. But that doesn't mean it's not important.
It's a good thing.
PS: I don't think this is available (yet) on wordpress.com.