Ever since I started riding a motorcycle I've started to believe this to be the case too. I get so many bug splats on my helmet, jacket, and motorcycle that I'd never have if I was driving a car. By the end of most rides out in the country on the highway I'm covered in splats.
i've noted less bugs on the windshield but about the same on the optics and the radiator screen, so i go with the aerodynamics explanation as well. bugs are there because i see the bug swarms around the road too.
Driving in the eighties with windscreens full of insects, and now hardly anything, and a lot less of the things that lived on them.