I don't know of any scientific, proven numbers on this - only what I see.
And what I see is a lot of bikes with less than 3,000 miles and several years old. Everything from Gold Wings to Beemers to Honda, Kawasaki, Yamaha, etc.
Just recently (nearly) purchased a 2000 Honda Valkyrie with less than 10,000 miles. That averages less than 1,000 miles/year for a 15 year old motorcycle.
Here's the scenario:
Guy buys a bike. Rides it 1,500 miles the 1st year. He is now a biker.
Year 2: Other things take precedent. Like is hectic. The bike gets another 750 miles.
Year 3: Bike is a little hard to start and runs a little rough because the owner doesn't know about fuel stabilizer and battery tenders.
Year 4: Bike won't start. After some amount of trouble and the help of six friends, the bike starts but runs like crap. It sits there for the rest of the year because
a. owner lost interest
b. It's gonna cost $$$ to put bike on the road, and he's just not that interested in the 1st place.... and
c. The wife thinks that he doesn't need that damned motorcycle in the 1st place.
These are the sort of bikes that I buy - mostly metric motorcycles.
I like a lot of different kinds of bikes, too, I have nothing against anything with 2 wheels and an engine. As for the people who ride them, well, they come in all types.
That's EXACTLY what I do, done it for years. Bought, fixed, and "rode and sold" a lot of great bikes over the years, learned a lot, and made a few bucks along the way.
In 2008 I sat on my first Versys, it fit me so well that I made a point to keep my eye out for a good used one. Haven't yet run across a used one I would buy, the damn things hold their value too well, and they aren't exactly common.
I have a (growing) list of bikes I look out for, and keep a close eye on the market, just in case I come across one that can be advantageously purchased. Fortune favours the prepared...
In 2013 I bought a brand new 2012 Versys from a dealer at what I considered a pretty good price. First new bike I've bought since 1982. I don't ride much, and I take very good care of my bikes. I could probably sell it today for what I paid for it. Which is good business. I learned a long time ago that the first offer I receive that covers my costs and gives me $1 profit for a vehicle, I should seriously consider selling... They make bikes every day...
That's adventure enough for me...