Wow...I don't agree with this at all. I use DME too but most of the time I book my flight for late in the day or early evening so my DME time isn't until hours after the 11am check out time. So if DME says I should be ready for pick up at 4:30 pm how is that going to help housekeeping know what time I vacated the room in the morning?
It only takes a moment to call and let someone know the room is vacant so I just don't see what the big deal is and Disney certanily wouldn't lose my business over it!!
We are always on a flight at 11, so we are on the bus before 9am. Disney knows this, they check us onto the bus.
For people who leave later than that, then bell services is presumably storing your luggage, and can let housekeeping know. If you took your own car and put your things into your car at 9am before heading to the parks, you probably should tell housekeeping.
Staff keeping staff informed is called customer service. Disney used to be good at it. If we let them off the hook, we have only ourselves to blame.