All the reviews are from when the GT72 was first released. They also likely reference the CPU as being a 4710. At the end of last year the internals were changed so, GPU's now come with 4GB (not sure but there might be a model with 8 still) but CPU's were upgraded. Lowest spec Gt72 has a 4720 now, the higher spec ones have the 4870.
Edit: So there is a model with the 4870HQ and a 980m with 8GB for £2300. Looks to be out of stock with no ETA. There's also the model I had planned to wait on with the 4980 but that's £3000.