You make several very good points. Thank you. It seems to me that we are dealing with two categories of criteria: 1) By virtue of our environment, we have adopted a sense of what a bicycle is suppose to look like, i.e., an assumption; 2) From the point of view of more objective (if possible) analysis based on the "rules" of composition and what comparative size triangles and circles look best together.
I agree that this thread is totally pointless. However, it did get me thinking about the composition question.
Here's the rub: "rules" of composition change depending on what you're doing. I've had this discussion with wall artists who fail to grasp comic books are laid out with a different set of underlying assumptions (wall artists tend to make awful comic book artists). They also shift over time.
And there are often other issues going on in aesthetic choice; it does not exist in a vacuum. Take New Yorker's assertion about the perfect shoe size. Having worked for more than one ad agency (mostly storyboarding) I can say that aesthetics are one of their very last considerations-- it's more about selling, and a big part of that is allowing people to imagine themselves using the product. Hence, you make the sizes of stuff very "average," because they will fit the highest number of people and the most folks can put themselves in the product. Simply sales, not aesthetic at all.
On bikes, I think we tend to find bikes our size most attractive, because one element (a very important one) of a bike's aesthetic quality is the ride. That is an aesthetic experience in and of itself, and if you can't ride it, you can't and don't get it. Pretty simple stuff.