I think people are missing the point here. Irrespective of the deposit amount, Columbia's ED is an honor policy. They require that ED applicants certify that they will drop all other applications and attend Columbia if admitted.
It's true that the policy is on-sided in some ways and could be considered onerous, but nobody is forcing applicants to agree to the policy. In fact, they specifically state that if you are not committed to matriculating if admitted then you should apply for the RD round and not ED.
The bottom line is, that if you choose to apply ED, you are signing your name to a promise that you will attend if admitted. Other than the deposit amount, Columbia has no real leverage to do anything about it if you go back on your agreement, so the real question is what value each applicant puts on their own word. Some people always honor their promises; others are comfortable going back on their word when it suits their purposes.