The PC getting "much better" graphics is debatable. Increasing screen resolution and using 1024x1024 textures in place of 512x512 isn't "much better". Much better would be reworking the shaders to strain current PC graphics hardware as much as it strains console graphics hardware. High quality bloom, tesselation for hair (and fur) as well as smoke and liquids (not to mention finer mesh detail), better shadows and atmospheric effects, etc.
It's also more than just graphics. The extra memory (both RAM and VRAM) and processing power can do a lot for world and gameplay design, too. A much more larger and seamless world, physics and puzzles to make your head asplode. There's a lot of potential that's going unused simply because it can't be done on consoles. Why not give PC gamers a taste of that potential while giving console gamers the best their system can provide of it?
Where the PC gets screwed is in stuff that would take a lot of effort to add. If it didn't take any effort then they would just do it.
Right, and that's what I'm saying. Cheap, effortless additions mean little. Proper meaningful "additions" take effort, and yes, it'll cost money. But IMO, that extra cost is worth it for that portion of your audience that would benefit. A company that was more concerned about making great products than maximizing profits would see that. I'm not saying a company should forgo money or profits, but they can survive without taking a constant must-get-moar-money-and-cut-costs attitude.