It’s a sign of things to come.
I would not be surprised to learn that the Haswell generation of rMBPs is the last one to feature a dGPU.
Broadwell will likely bring us a slimmer form factor and larger battery as well as graphics performance equal to the 750m, but without the dGPU.
The original plan was probably to do the iGPU-only switch with Haswell, but GT3e didn’t quite meet the expectations yet, so they threw us a bone with the high end 750m models.