Feel free to produce counterexamples if you can think of any.

As far as I can tell, Crysis is still the PC game with the highest hardware requirements? And if this is true, it is almost certainly the longest a game has ever retained this title?

Why do we think this is?

Is it the push to get high end games able to be run on laptops?

Have PC games hit the point where people don't care about improvements in graphics anymore?

Any other reasons?

The HD consoles are important for sales, and as such many multiplat PC games are made with consoles in mind.

By highest requirement you mean minimum requirements?

Because the people over at cytek couldn't predict the future brand names for the next generations of GPU's and CPUs. So i would assume Witcher 2, Shogun 2 pushes the game alot, Red Orchestra 2 pushes some limits.

PC exclusives have high requirements because they are pushing much more polygons than consoles.

Why?
Because they can!

Crysis 1 is old now. there are better looking/more demanding games out there released already

Add the fact that CPUs and GPUs didn't advance much in the last few years (though they got somewhat cheaper).

Metro 2033 and The Witcher 2 beat it