Future proofing. People have been throwing that fallacy around quite a bit lately.
NOTHING is future proof in the world of tech. That GTX 690? In a year, it'll be trashed by the GTX 790. That HD 7970? It'll be trashed by the HD 8970.
And the 4870 is quite outdated. The 4850 is only a bit better than my 6670 ddr3. And the 4870 costs as much as the 7750, which I assume will be about on-par with the 4870, if not better.