My view is that if people who are disabled are placed in the exit rows they are a hazard as they can potentially block the exit. By disabled I mean obese drunk or otherwise compromised. Able bodied people should be in the exit row so that at the very least they can clear the area and at the best can actively help others to get out.
I think the problem has little to do with airline staff and much to do with the booking process - and a worrying thought as noted previously an extra $20 for the airline - that is a lot of muffin tops in the exit rows!