I am certainly no expert, but I did find two articles that talk about how ED works. From reading them both (see links below) it looks like ED is not a legal contract but instead works on the honor system (with HS guidance counselors as the watchdogs). While nationally 97% of folks who apply ED end up at that school, legitimate reasons for deciding not to go after being accepted are that the financial aid that was offered failed to leave up to expectations (EFC calculator).Of course, this decision not to go would have to happen prior to applying to other schools. I do agree with others that applying ED should not be done without great thought and research. It is very important to determine whether expectations of financial assistance are realistic, based on income, assets, admissions credentials, etc. EA is also an excellent choice, if there is less confidence of affordability.
http://www.nytimes.com/2007/11/04/education/edlife/strategy.html?_r=0
https://www.petersons.com/college-search/ask-experts-early-decision.aspx
After looking at these articles and a few others, I tend to agree with @bopper that colleges probably do give typical merit aid to ED applicants.