Something to think about...

A good friend of mine just got her first bike. I was unavailable to ride with her so her hubby borrowed a bike from a mutual friend of ours. Definitely not a low end road bike, but somewhere middle of the line, with aero-bars. During their ride her hubby got a flat on the borrowed bike. Since they're new to biking they didn't know how presta valves work and ended up breaking the stem when they tried to pump up the tire. They felt bad and wanted to replace the tube on the borrowed bike, so they took it to our LBS here in town. I'm sure this bike was too big, and my friends hubby just had street clothes on...maybe a pair of shorts and sneakers to ride in, so the LBS owner questioned him. I think the exact words were, "Looks like a little too much bike for you, sir." (I got a giggle out of that!)

Anyway...that could explain a few 'mismatched' bikes and riders, but certainly not all of them.