When Murphy ('28 Aero) arrived at my door, I phoned up the New York DMV to ascertain its status in NY. After being shunted from pillar (sliding?) to post, I was connected to the "guru" of NY DMV regs. He first asked what vehicle I was calling about. After telling him, he evidently had an automotive encyclopaedia and complimented me on the "fine looking motorcycle." In NY any vehicle with less than 4 wheels is a motorcycle. When I then inquired regarding helmet use, he quoted a subsection of the vehicle statutes that if it had a cockpit, no helmet was required. I drove Murphy on a regular basis until I sold the Aero this May. Not once was I questioned regarding helmet use and I often was followed by motor officers. Now that my new M3W is a week or so from delivery, I searched the DMV regs on-line and have been unable to find the "cockpit" section.
As others have stated, no doubt helmet use is safer (But then likely not driving one at all would be safer still!).
Cheers & Happy Morganing!