While the rest of the industry have evolved their model lineup into modernity (since the 1970’s), HD continuous to (and successfully I might add) keep “revising” the same old models and often times goes back to the past in styling (note the model 72 and others). I honestly don’t know why people like that stuff and buy so much of it that HD is able to stay in business for so long. Don’t bother explaining this to me either because it would be like telling me a 1967 Mustang 289 is better to drive than a 2012 Mustang Boss 302.
BMW’s Mini is successful but it is a modern car with modern high performance that will blow away many modern cars today. The Mini does have some retro styling touches but you can tell today’s Mini is modern versus the 1970’s model! Compare today’s Road Glide or Sportster to the ones offered in 1996 for example. They look so much alike, it’s hard to tell the difference except in the smaller details. Of course the engine and chassis have all been upgraded but the performance only increased incrementally. The V-Rod was the only truly modern bike H-D has offered in recent memory. The XR1200 is the other one that is probably more like the Mini in its execution. Everything else is a re-hash of the same models.
I think you're missing the forest for the trees in some ways. HD has modernized its bikes but it's done so in ways that don't showcase the technology. Some of the stuff they've kept the same because the whole point of Harley is heritage and that "old school" look and feel. People don't buy a Harley because of water cooling or the latest cam technology. They buy it for different reasons altogether and just because you don't get it doesn't mean that it's wrong. Hell, I've got a motor that dates back to 1923 and I absolutely love it. It's not always about the "latest and greatest".
james