You said, "How would you feel if you had a medium-good computer and then be forced to pay $10 more for something you can't even use?"
Why would you be FORCED to buy it? IF your system can't handle it, there would be no reason for someone to purchase it.
If one wants to play on PC, and it costs 10$ more for everyone just for graphics, then it's better for the consumers if the same results were achieved through a DLC, so that those who can't use the new graphics on their computer (but still want to play on the PC of course), can still play the game without feeling cheated of 10$.
Although that would probably never happen, as, like said before, Bethesda would earn more by adding it from the start. And the consumers wouldn't be disappointed unless they actually knew about it