Well... my 8800GTX lasted 5 years for me, and I expect my GTX680 will last at least that long... so I can't say that I'm all that surprised with either company slowing down how often they put out a new card.
That said, I was looking forward to getting an HD8750 for our guest room machine. I won't run out and buy a 7750 when I know that an 8750 is right around the corner.
That is the segment they really need to concentrate on, since they are going for low power for mobile. Squeeze as much performance as possible without needing an extra PCIe power cable would benefit their Mobile R&D. It is also the segment that nVidia hasn't competed well in... the 7750 is significantly faster than the GT640... which is pretty impressive for a card that needs no extra power.