That's true enough... Graphics alone does not make a great sim.

A sim needs immersion.

Good graphics is just one way of creating a suspension of disbelief that immerse the player in a sim. But great graphics and bad framerates are bad for immersion. Flight modeling. Systems modeling. Intuitive controls. You name it! Creating the "feeling of being there" is a tough job for sim developers! It also comes down to your own imagination.
But, like Ice says, ground textures doesn't matter, if there's other stuff keeping you busy and focused.

F4 and its iterations sure have loads of immersion! That's for sure.