Originally Posted by LarryJ

It is not a new rule. The 50-seaters, E145 and CRJ-200 are handled differently than larger airplanes.

Small bins on the E145, of course, so the airlines that operate them will take that into account when developing the carry-on and weight and balance programs for those airplanes.

On larger airplanes, the weight of the carry-on bags are included in the "average" passenger weight used to calculate the airplane's weight and balance. The smaller airplanes can't fit nearly as much carry-on baggage on board so they use a lower average passenger weight and each valet gate-checked bag in counted as additional weight. Since the weight and balance program is not allowing for that extra weight in the cabin, they have to restrict the amount of baggage each passenger brings on board or their lower average passenger weight will result in under-estimating the weight of the airplane which has safety implications.