Good points on both sides. On the one hand, many (most?) wings are adjustable in steps of probably a fair amount over one degree, while the screw type ones would be infinitely adjustable (dial in 1/100th of a turn if you want). On the other hand, many people want finer adjustment for the sake of better tuneability, where the handling is ruined if you go 1 degree either way.
One thing to keep in mind is that on the wings designed for a specific real car, it's probable that the available settings were given much more careful design consideration than simply allowing 7,8,9 degrees (or 7, 10, 12 for that matter). Suppose a real wing was tried with 7,8,9 degree adjustments. The crews might have found that usually 7 wasn't enough, but 8 was too much. The aero folks might provide a newly redesigned wing with 7.5, 8.5, and 9 degree adjustments.
Perhaps the guys that want the finer adjustability are really the engineers in the LFS world. Why not allow the finer adjustments for awhile, then later on pick out the fastest set of 5 or 6 or whatever settings and keep those as the only available options? Might that eventually lead to the best of both worlds?