I thought CBS and Paramount had some form of gentlemans agreement that whilst Trek movies were being made there would be no TV show.
It makes sense for CBS to stay on side with Paramount with this because perhaps in the future a TV show will use the sets and props built for the movies?
Would it really matter if they didn't? There is no way to get a budget on a TV show to move nuTrek to TV.
Sets and props cost lots of $$ and would make a TV pilot or mini-series hugely expensive. CBS would have all the sets etc ready made and so the huge expense has already been taken care of. It would make it much cheaper and therefore feasible on a TV budget.
EDIT: So Paramount will have spent the bulk of the money that would've been spent on a TV Show on the movie and all that comes available for use in a TV show.
EDIT2: Paramount are considering starting up a TV division so maybe they can make a future show and sell it to CBS?