Last year from about May through Sept, put on about 3500, I expect to put on a bit more this year, with a couple trips to my in-laws and will probably see between 6-8K, most of my riding is just back and forth to work (I know not that exciting).
In general, a car average is around 12K per year, so I would guess the bike estimate assumes that most bikers supplement their cage driving with the bike. They fail to realize that there are many that are tourers, who do lengthy trips on their bikes. I'm not one of those yet...