I think everyone has good points on here but, really you guys are looking at it as if the universe is made out of one dimension.
For my 3-dimensional explanation:
Personally there are people who applied early, like JUNE, and got accepted to lets say their 4th choice or something like that, and haven't heard a thing from their first choice. They are obviously going to put down a deposit. (SCHOOL 1)
Then the same person here receives another interview from their 3rd choice school, and successfully obtains an acceptance. Well, they could either drop their 4th choice or keep it because they found out many pros and cons about both schools from reading SDN (which keeps updating itself everyday from everyone) Thus (SCHOOL 2)
Then it's March, the last run till you get that 1st choice. Let's say you got an interview but you are wait listed, OH **** now what? You are still scrambling to figure out where you want to go from your previous two choices. So as you wait longer, 2nd choice gives you an interview and then accepts you. OF COURSE you are going to put a deposit down. (SCHOOL 3)
Now are you really the bad guy? Are you screwing everyone over? Probably. But you didn't intend to. The system is messed up. But some people do have special circumstances. If they spent the time and money just like you did, and maybe more, why not let them decide? AACOMAS should change the May policy, but because D.O schools allow long periods accepting applications, it creates such a rift.
We can't blame each other. It's really the system.