Combine cabs may be pressurized more than automobiles due to the dusty conditions and, no doubt, the demand by us customers to want to keep that dust out of their $200,000 machine's cab. Add to that, the fact that car doors are considerably heavier than combine cab doors and have more momentum which may also aid in making them easier to close. I personally would rather have a cab door that needed a hard pull to get closed than one that let dust in - but that's just me.