So DX10 was a must?

[Porsche]

From the few minutes I am able to fly before the game crash's I think the ground looks good. I am able to have everything on high settings. I would think logically that if you want to have a game last as long as IL2 you would use the best technology available at the time of design. DX10 I have wondered as well what the differences are. I am sure DX10 allows more options than DX9 but what are they?