As far as the Facebook link provision, it just makes sense. Facebook is much more popular than Windows Live. Windows Live may have many accounts created, but among my list of contacts, the same people are much more active on Facebook than they are on Windows Live.
It doesn't mean that there shouldn't be a button to automatically create a link with a thumbnail, title, and description for Windows Live. You're right, there should be. As I said above, my vision for what *could* and *should* be done with your Windows Live contact list goes a fair bit beyond just notifying people of comments, etc.
To me, just that button to share a link, thumbnail, and description isn't nearly going far enough, though, so my point is just that Windows Live isn't missing out on much that Facebook is getting. Again, I'd like to see the synth embedded right there on my Facebook or right there inside of the Windows Live Photos page.