I'm surprised you too have made this mistake. Really, I'm sure you have the experience to know otherwise, sorry you failed your knowledge roll. Anyway:
You are correct that tipping cows has no inherent benefit to many people. This is because they do not represent a significant enough threat, therefore there is no CR by which to gain XP. However, for, say, a level one commoner tipping cows many certainly end up leading to enough xp gain to level. Then, by starting on the process to level further, a person might in the future raise their Int score, leading to greater perspicacity, spatial reasoning, and so on.