You've also got to factor in weapon speed, off GCD ability usage, attacks that use 2 weapons (DW Frost, Mutilate, SMF's Slam, etc).
in the worst case scenario, yes if you procced your mastery every attack (doesn't it only procs off auto shots) and procced the durability loss every shot and every WQ proc you would lose 90 Durabilty. However if time to failure or rate of durability loss is what you're actually looking at you need to factor in alot other things Mainly APM that use the weapon and proc a durability loss as well swing time. my prot warrior is likely to have a much higher APM due to him having to use off the GCD special attacks while doing his normal GCD rotation, and my sub rogue despite having few abilites that utilise her off hand will have it swingtime at around 0.7 seconds, which being as it only has 75 durability gives it a particularily low time to failure.
Hell what about shields, A prot warrior will nearly block every attack launched at him, on a fight with a crap ton of adds on him(such as magmaw)he's going to have upwards of 20 adds on him each attacking every couple of seconds or so, and in addition he's gonna be attacking with his shield approximately every 5 seconds aswell