Ok, so you've designed this grand glimmering SOA, and you have a few dozens services each assigned to a development team.

As the iterations spans the contracts have to be amended (be that WSDLs, plain old messages, object APIs or whatever) - do not leave the task of changing, aging or maturing to your developers, team leads or anyone else - I strongly believe that the architect, having defined the boundaries between the major components (services in this case) is the one also responsible for the space between the services. Anything that travels this space is in the realm of the architect*

In my opinion, failure to be in charge of the contracts can result in major breakage of the architecture (chatty interfaces, security problems, services dependency to name a few of the possible and likely problems)