I haven't quite figured out why everyone worries about "who owns the model". This (much like when people think that BIM is a software!) is one of my BIM pet peeves.
Normally, I don't think about this at all; for me, it's a non-issue. However, this came up today at a meeting with a non-BIM architect who is interested in implementing.
If anyone "owns" the model, it's the building (therefore, the owner). As I've stated on many occasions, I believe that all of the project participants should be able to extract information as well as add information to the model. I don't understand the concern that some have about collaborating and sharing which relates to what I think should be the goal of the team.
I think my new answer to this question will be: who owns the construction documents?