Actually Globaliser none of those people that you cite have actually said anything about the load capacity of overhead bins, one poster did and made a ridiculous statement which you are somewhat justifying. The safety stuff they talk about is regarding items falling out of bins, etc. not whether the bins can take the loads or not. Knowing something about the rated and actual loads, Even 5 bags at 18kg each in a bin are within the design limitations of every bin on every jet (bar the MD80 series and Bae146 series) currently flying in the world (I cannot imagine more bags weight put in one particular bin in any case, bin of course being defined as either an individual bin or strut to strut.