My take on the "Why do so many American boats have wheels" is simply...
1. Most people who by brand new boats in America are not really sailors, just people with money looking for something new to do. (Not all, but most, as evidenced by all the new boats that never get sailed)
2. To a non-sailor, tillers are old-school and low tech. Seeing a tiller makes some people wonder if they are still using natural fiber sails and tar sealed wood hulls as well. Wheels are new and high tech and fancy. Cars have wheels, power boats have wheels, why would a sail boat be stuck in the old days of a tiller?
3. If the people with the money are turned off by the sight of a tiller, then no tillers will be installed, regardless of all the finer points either way. Most large manufacturers will go with what sells first, without regard for which would be better for this particular hull, shape, size, weight, design of boat. Only your more specialized manufacturers who tailor to the real sailors with lower volume boats will take that into account.
Not saying wheels are always bad, and tillers are always good, I think the points of what makes sense and when have already been covered by far more knowledgeable people then me. But for me, I am happy with the tiller I have, mostly because it is on the boat that I have.