As a Flight Attendant I can tell you that carry on bags are a huge problem in my flying day. My philosophy is "you pack it, you haul it" and I make sure I stick to that rule with my flight bags. If you are injured or for some reason unable to lift your bag and have packed appropriately (ie lightly) then I dont mind assisting. However, if we fly say 3 flights a day, with 170 plus people on each flight, that can potentially mean a a lot of lifting for us and potential for injuries. I can tell you that one of the highest injury rates for flight attendants is lifting injuries!
The only time I see "measuring" going on is visually....we can spot an oversize bag at a distance as can the gate agents which is when they will usally measure the bag.
I use either a 21 inch travelpro rollon or a 22 inch both of which fit wheels in to an overhead bin.....do not stuff the outside pockets because no matter how much you want that bag to fit and no matter how much you complain that it fit onthe last flight..it wont fit!!!!.
With fuller flights and more people opting to carry on bags I would personally bring on a smaller bag which can fit easily or at least get on the aircraft first!
Oh and be nice to your flight attendants...its not our fault that your bag wont fit...and you never know we may find a secret little spot to put that bag in!
Happy travels