In the mid-1980s, he said, Congress tightened rules about how much money can be written off on luxury automobiles used for business -- but excluded vehicles with a gross weight of 6,000 pounds or more, partly an attempt to help farmers afford tractors, large trucks and other heavy equipment.

This is the sort of half-assed lawmaking that pisses me off. If they wanted to give farmers a break for buying tractors, et al., then why wasn't the law written that way?