Or maybe they simply don't get the same ''OPTIMIZATION'' treatment that console get. A 8800 Gt was like 4-5 time more powerful than a PS3. Yet a game like uncharted would never run on such a card. Untapped potential is real.
well, every PS3/XBOX360 (current consoles as well, of course) had the same hardware, so its very easy to optimize a game for it. and now try to imagine how many combinations of CPU and GPU are possible with only the PC-hardware of the last 4 years. its impossible to optimize a PC-game as good as its console version.
The truth is somewhere inbetween. While it's much harder to optimise for PC due to the large potential configurations, many developers don't have the time, money or desire to put in the effort.
While it might suffer issues at the higher end of the scale, GTA V is remarkably well optimised for low/medium range cards. Console GPU equivalents in the R9 270(x) and the GTX 760 can easily achieve console level fidelity with much higher framerates. Metal Gear Solid: Ground Zeroes is also another example of a well optimised game, capable of 1080p/60 FPS with even very old configurations.
A game like Dark Souls II is also light on graphical demands for it's fidelity, with older flagships like the GTX 680 perfectly capable of 4K gaming.