I guess Robinson's red zone looks (and overall receiving numbers) have to go somewhere. I'd hope Dez will finally make that leap, but that's far from a guarantee.
In reality, Robinson's inflated numbers last year were more of a result of the immense attention paid to the three guys you mention than anything Robinson did.
It'll probably be a wash across the board. The new WR3 will get some of it, Dez some it, Miles some of it (remember he was hurt a good portion of the year), and Witten some of it (to a lesser extent than the other 2 IMO).
Muddy enough answer for you?