This is one area where some of the rules and policies make some sense.
The weight limit on hand luggage is as much for safety reasons as it is for storage and convenience issues. The main point here is that during extreme turbulence or even a 'survivable' accident, many injuries are caused by loose items of hand baggage flying arount the cabin. It's incredible how much kinetic energy a 10kg piece of handluggage can accumulate in a very small distance during a 2g 'bump'. I had a simple proposal for those passengers that wanted to take 20kg pieces of H/L; If they were happy with me throwing that item at their head, they could carry it on. Few said yes, but for those that did, I explained that I was just making a point and the safety of others would mean it would still HAVE to go in the hold.
Applying common sense was always the order of the day; if the flight was full, the piece and size limits were adhered to or the boarding would be seriously slowed as people fought to find storage for their items, often delaying a flight. When the flight was less than 3/4 full, some relaxation was allowed as long as the reason was relayed to the passenger. When business class seating was spread out (3/3 seating changed to 3/2 or 2/2 seating), the realtive increase in overhead bin space would allow us the let businessmen carry their briefcase, suit carrier and laptop in the cabin.
There would also be compassionate allowences for families with small children and special needs passengers.
This could be done because these were scheduled airlines with relatively good seat pitch and business class sections. However, when you are talking about a low cost carrier like RyanAir, where the cabin configs are high density but the overhead bin space is not; they must stick to the rules especially on full flights, or risk stupid delays because the cabin baggage cannot be accomodated safely.
You pays yer money, you gets yer choice. If you want some leeway on handluggage, fly a scheduled carrier that could facilitate such leniency. Low cost carriers just cannot do that in most cases.