I, too scratch my head when I see bikes with very low mileage. But, like has been said above, everyone has their own priorities.
One thing that I think I've noticed (not very scientifically) is that there have been FEWER of these low-mileage bikes. I watch eBay and craigslist occasionally, especially when I'm getting ready to buy/trade. I feel like I see more average to high-ish mileage bikes than I did 8-10 years ago.
It could just be my imagination, too.
Personally, I do remember 1 year in particular where I only was able to put 1252 miles on my (then Road King). It is tough for young parents who are in the middle of hatching new offspring! Even now with teenagers, I don't ride as often as I'd like because it's tough to pack more than 1 passenger on these bikes!