That really isnt fair. I've never known a helicopter pilot who could not fly a fix winged aircraft aka cesna or something. People usually get there single engine first.
I know several, but this isn't the point. The point is, you have two people who do two things that, while similar, are very different.
This is a small-scale example:
My brother races motocross (nothing serious; just a hobby--whatever C or B class means). Have him putt around the neighborhood or on low-speed roads on my ZX6R, yeah, he would probably do alright. Get him up to speed (say on a track, twisties, or even a curvy highway), it might get sketchy (for example: counter-steering and leaning aren't a part of what he does).
I have a ZX6R, and while I have never tracked it (yet), I went dirt biking a few weeks ago with my brother. I did alright; I pulled a few jumps and dumped it a few times. However, throw me into a race, and I would more than likely fuck myself up. Pinning the throttle to keep the rear spinning or putting a leg out aren't what street riders do.
So what this boils down to is this: while they're both very similar, they both require an entirely different set of skills.