I think it has a lot to do with the IMA warranty period and the fact that Insight's are usually bought as a car to put a lot of miles on. I believe there was a gentleman that occasionally visits the Yahoo group that put 100,000 miles on his in just a little over a year. They bought the car back and gave him another and he racked up about that many miles as quickly on the second one.
I think a lot of the high mileage Insight's you see on there with only so so LMPG's are just driven, not necessarily hard but fast at 75-80mph highway speeds. So that's not necessarily a bad thing.
Gee now my 36K miles seems kinda low in comparison.