Why is the PS4 only 4x as fast as the PS3?

Two assumptions:

1. The quality of graphics/visuals depends mostly on texture detail and the polycount
2. The texture detail and the polycount a system can render heavily correlates with the floating point performance of the system.

The ps3 had 64x the single-precision flops that the ps2 had. they had 6.5 years, which translates to a ~20x expected increase (Moore's law).

The ps4 will have 4x the single-precision flops that the ps3 had. they will have had 7 years, which translates to a ~26x expected increase (Moore's law). However, the cost is also about 33-50% less than previosly, but this doesnt account for a facotor of 6 difference in performance.

Why is the jump of next-gen visuals smaller than in the past?