In my opinion, there is a very large difference between EN and EE. On a scale of 1-10, EN is about a 1 or a 2, and EE is about an 11.
People who join EN groups, or who post EN groups, might very well be making a sound decision based on their character's abilities. I have a character that can solo (some) EE's, but not all my characters can do so. Some of my characters just don't have great DPS, and they do fine in EN, but they are either barely contributing in EE or they are riding around in someone's backpack as a soulstone in EE. With those characters, EE simply isn't any fun for me, because it mostly consists of "I have to hit each mob five thousand times for it to die, but if it hits me two or three times I'm dead. What fun!"
If I post an LFM for EN, or for EH, I'm not going to change it EE once the last guy joins and complains, "I want to do EE, I have a streak, I need it on EE for saga, I want the EE version of the shiny in this quest, I want the extra XP, etc..." I just think keeping the posted difficulty is the courteous thing to do for the other people in the group. If they joined my LFM because it was posted for EN and they know they can actually play DDO on EN (as opposed to either spending the quest as a soulstone or contributing infinitesimal amounts of damage through every fight), I don't think it's fair to switch it to EE and leave them up a creek.
However, this is something I see other people doing often. Not all the time, but often for sure.
Would it be considered acceptable if someone joined an EE group and then started complaining that EE is too hard and they would really prefer EN? I doubt anyone would think so. Why is it acceptable with so many people to join EN or EH groups and instantly start complaining that the posted difficulty is too easy and they would rather do EE?