Money is money, but a deal is a deal. If you buy or sell some other product or service, would you be pleased if your counter-party backed out of the contract afterward? A student applying ED should know that s/he agrees to attend if admitted ED. S/he should also use the school’s net price calculator before applying – ethically, s/he should not back out unless the school gives a much worse financial aid offer based on the same financial parameters as the net price calculator run. As with any deal, one has to do prior due diligence to see that the financials of the deal are desirable enough to commit to the deal. If one does not want to commit before comparing offers, one should not make a binding commitment beforehand.
Of course, W&M’s punishment of the following students at the school creates the situation where the dishonorable ED student can back out without penalty for himself/herself, while causing the punishment to accrue to innocent third parties.