Methinks that the working set and non-working set line is bullshit. Just because you don't take a particular set to failure doesn't mean you didn't do the set.
nah thats not quite right,,, its a different mentality, all joking aside you just breeze through the warm ups then go hell for leather on the last one
until you try it for your self youl never understand, and if you do it propperly you wouldnt feel the need to do another few sets
you also have to have perfect piston like form and the will to force extra reps out
its not the only way to train tho, just another way to skin a cat