I don't really see any huge "competitive advantage" for sites such as Facebook from "being seen to be open".
The main fear for Facebook comes from remaining closed and self-contained while a competitor such as Myspace becomes a sort of open ID for the web.
Most likely, Facebook will be in a much stronger position if they are able to establish that cross-web position for themselves, but that's still a risk for them to take. Leaving that risk for Myspace to take is an even bigger risk, however...