Just to throw another chunk of debris into the mix: Q is not just about pedaling comfort or efficiency. There's also the issue of cornering clearance; a low Q improves cornering clearance. With clips and straps you can only get a pedal so narrow before losing some functionality. Until indexing came along, front derailleurs were very simple, using a flat outer plate; derailleur clearance wasn't much of an issue, so the crank could turn very close to the frame, only having to clear the chainstays. This would have been a strong influence on design.
With modern designs, on the one hand, pedals have ceased to be an issue in ground clearance or cornering. On the other hand, front derailleurs have shaped plates and need more clearance between the big ring and the crank arm. The whole issue of frame stiffness being highly valued has added another influence--it's helpful to have beefier chainstays set as far apart as possible, and to have bottom bracket bearings set as far apart as possible. All these things make it easier to design equipment based on a wider Q.
Another issue is rider size. The smaller a rider is, the more Q matters. Overall, as with the rest of the population, riders are undoubtedly taller overall, so this issue isn't as meaningful as it once may have been.
Bob Schenker
Oakland, CA USA