yes. i change every 100hrs which is what my mower manual says to do. i use synthetic though. if i were to use regular i would do it more often. it's not about being dirty it's about the oil not breaking down. would you be fine to run regular oil 100hrs? yes but it will be more broken down at 100hrs than synthetic oil would be.
We all change oil but we barely clean the cooling fins That is # one engine killer