PAXboy I think the EP's gripe is that they see it as another way for the LoCos to gouge the passenger who turns up at the airport with a slightly out-of limits bag and is saddled with a hefty checked-bag fee - or indeed a lady with a handbag as well as a 'legal' cabin bag.
The fact that differeent airlines have different limits and even within an airline, staff at one station may interpret the rules differently to those at another station is an irritant.
I don't fly LoCo but I know I would stress massively about the size of my cabin bag, I just don't need that kind of hassle.