A serious endurance cyclist or swimmer will certainly go through 3000 kcal on a normal training day if not more.
I've burned an estimated 5000kcal daily on the bike for weeks. What's more is I know these numbers are very accurate as we train with power meters that record our energy expenditure with minimal error.
It's important to distinguish between serious athletes and average people who exercise. It's possible that truly competitive athletes - for instance, who run 120 miles a week to your 30 - will be much more likely to get ill from their efforts. It can take serious fitness - and a mentality acquired only by years of serious training - to push yourself to the extent that you fall ill, and maybe the recreational "athlete" described in this text can't reach that point.