No, I mean they all wear helmets. Cycling as in road cycling, group rides, as a sport, not for transportation. They're not professional cyclists, they all have other jobs.
I find them very annoying, they tend to be very inconsiderate. Cycling on the road where bike lanes are available, and when they are on the bike lane they tend to be agressive to normal cyclists if they don't move along as fast as they want.
They're not all like that but many of them are, which leaves a bad taste as soon as you spot these groups of wannabe lance armstrongs :P
Also, anecdotally, I am occasionally road cycling for sports and do wear a helmet at all times. However, I am certainly not doing that because of aerodynamics.
Edit for clarity.