A part of the problem with luggage is the complete indifference that United have towards their own rules and the lack of enforcement. This pleases some people. Annoys others. I much prefer the consistent application of simple rules. Interestingly doing OLCI for my flight today for United, I had to check the box that says "do you accept our carry-on policy" which I did. However, there will be no enforcement of it so what does it matter?