I do find it weird that you see a lot of very high mileage Harley's and BMW's but only a smattering of high mileage Japanese bikes. The only thing that I can figure is that people tend to buy Japanese bikes as their first bike and then graduate to Harley's and Bimmers. So the Japanese bike stay with the less experienced riders, and thus are crashed and totaled before they ever get the chance to become senior citizens.
BMW's and Harley's exude a certain quality about them that attracts seasoned riders.
Now with that said, I'm a dyed in the wool Japanese motorcycle man. Spent my whole life on Yamaha's which ran flawlessly, but now find myself the proud owner of a couple big Kawasaki's...ZZR-1200 for the street, and a KLX650 for playing in the dirt.
When I ride BMW's I'm always struck how solid they feel and stable the ride is. But they never accelerate, brake, or turn as well as the Japanese bikes. And there's nothing smoother than a Japanese inline 4. I consider it the perfect engine...especially the one in my ZZR; magnificent.
Harley's just have class and a nearly perfectly executed finish. But the iconic 45 degree engine just puts off too much vibration. And at some point that vibration will cause some problem.