To me, the siloing is as much about how seamlessly the social graph commutes across different services, or rather in this case does not. Perhaps you are right, that their use of XFN and FOAF will directly address that barrier but I am skeptical. Both have been around for a while and I have yet to see an effective application towards making my life as a user easier. Instead, they seem to extend the cost of re-entering my profile data into also re-entering my social graph with each new service.
Their response on pushing data back out directly, rather than through regurgitated feeds, was vague at best. FriendFeed at least did a somewhat better job of this though it was far from seamless. Also considering that idea of seamlessness, what about OMB and/or direct federation with StatusNet? Not likely but still would have been a welcome effort. For me, that is becoming a common refrain. Even when Google re-uses open standards and components, they build their own ultimately separate offering. This isn’t the first time, nor is it likely to be the last.
I would welcome a social aggregator or dashboard, I really would. If I had something for social messaging as useful as Reader is from feeds, I’d be delighted. Anything else in this space just feels like an annoying me too, play. Buzz simply has a lot of standing inertia to overcome to make the investment on my part as a user worthwhile.