“Clearly, more people would apply ED if there was an edge.” I disagree. I do think NickFlynn is correct although I think 50-75% is too broad a category and if you are at the 70th% your odds are not the same as 52% but are close to 75%.
Also if you are at the 70-80% for every school with all boxes checked (class president, non recruitable varsity athelete, debate captain, head of food drive, all of these not just one), no blemishes that are obvious. There is a tremendous temptation to see where you will end up. Will you get a HYPSM, will you get a free ride at Duke or WashU or Rice.
While a few people who are particularly good at presenting themselves in an application or have small hooks at certain achools will end up with those, most RD people will be on here next April complaining that they did not get in any place they really wanted to go and now have to go to CMU or UCLA (I know good choices but these people were envisioning Penn and Columbia as their fallback). The reallu unlucky will have to go to theirstate safety (either the honors program or free ride but not where they wanted to be).
Finally committment is scary. I went from school to school last summer and they mostly looked alike to me. If one had stood out I would have applied ED.
As for Bates, did not apply cannot say. I have heard that about Amhearst as well. That is part of the research the OP needs to do. However, schools like Vanderbilt are taking 50% of their class ED. I doubt everyone there is a legacy or good with a ball bat or speed record.