Here's someone with big arms and wrists, in an advertisement that was presumably meant to imply that the oversized product is the more "manly" one. Which watch would you say looks better?
With regard to generalizing about people and their clothing, say slim vs. full silhouette, hard vs. natural/soft shoulders, county vs.city colors...there is a commonality no matter what the silhouette, shoulder, etc...they all have a size based on the human body. Sure you might go up or down a half size to a full size depending on the maker and cut. But its highly unlikely that if you wear (using American sizes, I know a European 52 jacket is about 42 US) a 42 reg when wearing say a Hickey Freeman suit that you will go to a size 52 US in a Brioni or a RL Purple Label. You might like a larger full silhouette, but going up 4 sizes is generally not going to be the answer. Sure if you like billowing pants instead of buying a 34 waist you could buy a size 40 and cynch it with a belt around your waste...but its going to look silly and like it belongs on someone else. On some level its the same with watches. A really skinny guy that's 6' and weights 180 lbs is going to look silly wearing a 45+mm watch...he just isn't going to have the bulk to have it look right. Sure he can do it, but he might as well also start buying shoes and suits that are a few sizes too large to complete the look. I'm not saying it would work better on a really short fat guy...but there is probably a reasonable size range by which watches will look good on someone...too small it looks like the guy borrowed his wife's watch, too large and the guy need's to grow into his Daddy's watch.
I'm not sure watch aficionados overemphasize the aesthetic value of prior generations...although I think they often overemphasize that quality was better years ago. As for how future generations will view the big 3 or Rolex...I think they will still continue to be a strong influence on the market for luxury watches and what people buy. The big three and Rolex have all been around for over 100 years (more than 250 in the case of VC). There was a slight shake up in the 1950/60s when VC was no longer considered the top of the big three and Patek took that place in the minds and hearts of many. Names like PP, AP, VC have a reputation...something like that of legends, things that are considered the best and owned by people that are successful. I don' really like car comparisons...but think of it this way...Ferraris are cars of legend to most people. In the early 90s Acura came out with the NSX, it was revolutionary and was considered the best car in its day. It made Ferrari, and others rethink what they were offering people. But in the end, the NSX is an interesting footnote. Companies like Ferrari, Aston etc...rebounded and came back stronger. Sure they improved their products, but they offered legend, mystique, lore, and heirtage that upstarts don't have. Even if good companies like Breitling, Zenith, or Hublot increased their quality levels, reduced production to be more exclusive, and tried to take the position of Patek, AP, VC, I just don't see it happening...any more than we would see Acura becoming the most valuable cars at auctions over vintage Ferraris.
I took your analogy in a different direction because it seemed to negate that no matter how one nips, shortens, or modernizes a suit it still has a size. People of all sizes and shapes can wear softer shoulders, shorter jackets, and cooler colors and overall it will probably look fine provided they bought a size that fits them. Perhaps you took my buying the wrong size suit too litterally. I wasn't advocating it or suggesting its a coming trend, I used it as an example that size relative to a person's build matters. No matter how fine a brand you buy, if it does look like its your size its not going to look good on you. As for your suggestions that a traditional 36-38mm dress watch is analogous to a conservative tweed/flannel...seems to forget that 10-15 years ago most companies dress watches were somewhere between 32 and 35mm. The original Lange 1 at 38.5mm was considered very large when it was first released. In addition most Calatravas were well under 36mm until around 2001/2002 when they started making a few watches like the 5134 Travel Time in a 37mm case. So the 36-38mm or larger dress watch is a relatively new phenomena.
As for cars, yes an imperfect analogy, however, just as one doesn't buy a Patek because they need to know the time, one doesn't buy a Ferrari because you need to transport groceries home. Each is purely a luxury. A Ferrari is hardly considered an example of advanced engineering that is integral to daily living. Patek isn't priced to be a young persons watch, any more than Ferrari is priced to be a young persons car. I also don't think Patek's target audience has ever been people in their 20s. I don't know about you but when I was in my 20's and early 30's I had no interest in Patek, and they did just fine without my business. Now that I'm a bit older some of their designs are more appealing to me. As for what has created the legend,lore, mystique, be it for a high end watch or a high end sports car company...it may vary, but one thing that does not is that their legendary status has helped make them items that are often purchased not just because of their engineering, but often because of less tangible qualities such as beauty, rarity, and because they are seen as a mark of success or achievement. Brand recognition is a very powerful tool for a company, and Patek has it. I think it would take some tremendous mistakes for them (or AP & VC) to lose their status as the big three. They've existed and been known as the big three for about 100 years and I doubt that will change, just because of a younger generation.
I learned a lot about watches from my father. His beliefs as to what the best brands were/are made a very strong impression on me. While we differ in taste on certain watch models, we both tend to share a great deal of admiration for the same brands and have had a lot of input on the direction that the other's collection has moved. Interestingly, he has 2 watches that are larger than any of mine, but both are rather classic in overall design.