I agree that date formats in the United States make no sense. I would much prefer yyyy/mm/dd or even dd/mm/yy over mm/dd/yy but that is "above my pay grade" so I work with what I have.
In Site administration -> Language -> Language settings the language is set to "English - United States (en_us)". I have searched though the Language customization and have not found a place to change the format of dates. From what I can tell, this only allows me to change the terminology. Please let me know how this can be changed though the installed language pack as I am either blind and can't find it or its not there.
In excel the only way that I can get these dates converted to something that it understands is to split the column on the ", " and then concatenate the columns together again without the ",". I have tried a custom date format but the comma gets in the say for some reason. Maybe this is because I am not doing it right, or I have the US English version of Excel and Microsoft, in their infinite wisdom, thinks that I don't know what I am doing so they won't do what I ask for, or maybe Excel just can't do it.
Not to complain about open-source software, but I would think that if I choose the English - United States language package that dates would be presented in the format standard to the language that is selected.