All I know is that five years ago when the first film was being put together, some of the conversations on this board revolved around potential sequels. So, we fans certainly felt that sequels were in the cards if all went to plan for Abrams. I'm sure Paramount felt the same way. I remember discussions on this board about how long it would take to make three films, and how old the actors would be by the end.
I'm not sure where this idea that while they were making the first film they felt it WOULD be a one-shot deal, because I remember (albeit as someone outside of the production) the opposite feeling being true while this thing was in filming and production.
I remember people cautioning others who talked about sequels. They were right to be cautious, but the point is that the general feeling among fans was that if this film did relatively well, there would be sequels. I could be wrong, but I think Paramount was on the same page as the fans.