5 Durability is always 5 durability. It doesn't change its value. It's not like 5 hitpoints. You have 5 hitpoints, you can alter the rate at which you take damage (with a protection spell, etc.), or change your combat tactics (get farther away from the enemy) and keep on fighting in a different manner, and live. You can even take a hit and still live (see protection spell, above).
There is absolutely no reason why equipment durability couldn't be handled with as much depth as a character's health. Hitting a wizard in robes, a guard in mail, and a stone golem should all have very different effects on your weapon, and a rapier and a mace should have very different effects on armor.
"Holy ****, that greataxe is going to cut right through my shield - better have the rogue take that guy from behind."
"Hammering at that guy's armor with my blade is going to dull it in no time - better just stun him with a pommel strike then scoot past him."
"Dragonfire? Yeah, goodbye gear - better wear the cheap stuff, or maybe go unarmored and dodge the blasts, he's pretty slow."
Sounds like it would add a whole other tactical level to combat, right?
Sounds more fun than just dropping by a blacksmith every five fights to pay a few silver, right?
But the only ways to mitigate it are to use your equipment less (avoid combat, which also isn't very fun by itself)
I hope very much that won't be the case with Project Eternity! One pretty big factor in how much I like an RPG is how interesting the non-combat options are, so if a game is to-fight-or-not-to-fight rather than to-fight-or-sneak-or-charm-or-trade-or-xyz, then it won't be a game for me in the first place.