Yes, most relationships have some sort of power imbalance (although historically that has been drastically decreasing). What makes work relationships different is that it is hard to change jobs.

If you decide to go date a rich man on Tinder, you can break up without significant consequence to your income or your career. But if your boss asks you out you may face severe career consequences just for saying no. If you say yes and then break it off, the risks to you go up.

This rule has no assumption of guilt. It's just acknowledging the risk to the company and the people involved.