Dunchess
I am sure opinions will vary but I think that you would not want to bring up that other schools have dinged you. Not that anything is wrong with getting dinged, but my opinion would be that you don't want to highlight that other top schools have decided not to take you on because you have a low undergrad gpa.
As for whether or not to reach out...as long as you don't make a pest of yourself, why not. Let CBS know they are your top choice, let the adcom know that you have visted the other programs and feel the best "fit" with cbs. I am personally on the waitlist at CBS now, they have changed the waitlist policy and no longer want to hear from candidates unless they contact you. That is probably reflective of the tone of CBS in general but finding ways around that are possible, having a recommeder reach out to the committee or scheduling a visit and dropping by the admissions office know to let them know that you "fit" with the campus is a good way to show interest.
Thanks for the excellent guidance, Dunchess. Will let everyone know how it goes...