Most successful games don't require high end hardware to run. See all Blizzard titles for examples of this.
Blizzard makes games that can run on your grandma's PC because they hope that your grandma will give those games a try. And unfortunately, that's exactly what happens.
Making games that scale up and down equally well is time-consuming and difficult though. Because the idea is that the game looks and performs decently at both ends of the hardware spectrum. It's really much easier to make a game that performs well on lower end hardware and add in a few features that high end hardware can utilize rather than looking to monopolize the full power of top of the line rigs.
The things is that even the next generation of consoles aren't looking all that impressive on the hardware front. And very few developers are making games aimed squarely at the PC market. And even when they do, they seldom want to target the high end hardware segment. You're not going to find a Hard Reset or Serious Sam 3 popping up every day.