I think some of the reason for round count is that is how people determine when to cleaning (every 500 or 1,000), when it needs to go to a gunsmith for a checkup (I have only had one gun go to a smith and that was because the safety switch broke while I was sighting it in. So I took it to a local gunsmith (about 50-75 from home), told him that the safety switch had broke (popped of where it came through the stock) please fix and check all the connecting parts!
I think those who do maintenance by round count have been in jobs where their life depended on the gun going bang each and every time they pulled the trigger, military, high end LEOs, undercover types.
I do know some guns require cleaning at lower round counts than others. I have pistols that I have cleaned once in the time I have owned them with no issues (aka malfunctions). I have another that started malfunctioning at a lower number of rounds than the others had on them.
I saw a guy on the net who said a gun should be cleaned every +/- 500 rounds or when the gun begun to malfunction. He added, "So mine are cleaned every 500 rounds because in former life I needed my gun to go bang every time I pulled the trigger!" Not sure I would be that anal, but I think every New Years, Birthday, Saint
Rose of Lima Day, Saint Barbara Day, or Saint
Michael the Archangel Day (chose one) would be a good Idea, depending how often you shoot; I know a guy who shoots almost daily and shoots 1,000-2,000, he may want to clean after each days shooting.