Fuel Filter Change Interval

I do all the filters (air, oil, 2 fuel) everytime I change the oil which is about once a year. The same goes for the Generator too. Im doing the differential next week and Im actually changing out the hydraulic fluid and filter.....the guy at the parts store said he never sells any of the reservoir filters cause hardly anyone does this change although I know Brett has (Wolfe10)...Ive seem it on different WEB sites. I know, Im rambling on...sorry :B