There's all different kinds. You've got the 'weekend warriors' who take their bike out on a nice sunday afternoon if the weather is mild and dry. Others who commute with their bike rain or shine, still others who don't even own a 4 wheeled vehicle!
Heck, I even know people who NEVER commute but have over 100,000 miles on their bikes, which are only a few years old, because when they go out on the weekend, they really go somewhere!
My 900 had 8,000 miles on it when I bought it in September of 2011, and it's an '06! It's got 21,000 miles on it now!
Nothing against the people who don't ride very often, but man, I guess, I just can't imagine not putting a lot of miles on your bike! I don't commute to save money, I commute with my bike because I love the fact that on a busy work day I can STILL get a little riding in! (Plus I like to take the long way home to unwind!)
Although, seeing cruisers and stuff like that with low miles is one thing. Seeing mega-tourers like a Goldwing with low miles is really a head scratcher. Dealership I bought my bike from had a 1995 GL1500 on it, being sold by the original owner, with 5,000 miles on it (FIVE THOUSAND, not a typo). So you spend that kind of cash for that kind of bike and don't ride it? Different strokes I guess!
But +1 on the buyers remorse buys. A guy I used to work with got a killer deal of a Harley softail. It had 300 miles on it, and was a 2010. Lady bought it to upgrade from her sportster, rode it a few times, then finally sold it. She just didn't like it as much as she thought she would. (And you know how some of that Harley crowd is, there are tons of awesome mid sized cruisers out there that she could handle, but, if you ride a Sportster, the next step is a Softail, no way would they be caught riding a metric!). Basically brand new, but for the price of used!
When I was a freshman in high school my mom bought a car like that. Had 1800 miles on it, and was a previous model year. Got a KILLER deal on it. It was a Honda Accord, the two door one with the sport engine in it. Someone bought it as a mid-life crisis mobile, but then decided, they really needed a sedan. Came back and traded it for the 4 door Accord. Got a sweet deal!