The heat bloom of an Apache in motion is not necessarily near the fuselage. They are harder to take down with a SAM than you might imagine. Plus, flying nap of the earth, I understnad they are barely in the flight envelope of a Stinger.
Having written all that, I agree the threat must be greatly diminished.
p.s. The Apaches are like flying tanks-- best supported by, and supporting forces on the ground. I think we have half the story here.
They can be used as a standoff platform, "under" the horizon, with proper ground support targeting. That neutralizes the Stinger threat, the bearer of such weapon having no way of knowing where to aim and shoot - there is no visible target.