LOL! You make a good point on why thieves don't get plate-mail. It kills their stealth aspect.

just stand back at a distance and throw your knives

thieves DON'T melee. they hit and run with sneak attacks :P

Maybe it should be a combat talent.

One of the several reasons I left WoW was people actually trying to campaign for this... Imagine this conversation extended over 15 or 30 minutes.

"I just don't understand why we have such low armor and hit points!"
"Beeeecause you're a rogue?"
"Yeah but Warriors get all the way up to plate!"
"Right, because they're warriors, they're front line heavy hitters. You're a rogue. A rogue is a thief, an assassin. Your purpose is to sneak in, do your job and get out."
"Yeah but I die so fast!"
"BECAUSE YOU'RE NOT SUPPOSED TO BE GETTING HIT A LOT! You're not a tank! YOU'RE A FURGIN ROGUE!!!! Shit be thankful you have LEATHER armor, mages and priests get CLOTH! *storms off*"

Hehe I can understand that. Ahh if only there was some rouge magisheald armor. Something that would lower at least 15% of the damage. XD

well I don't play wow, but I do play a lot of other RPGs and I can understand both sides of the argument, honestly? I'd prefer to keep it at the leather level given that I'm closest to a rogue archetype in real life and can appreciate the pointlessness of heavy armor for such.

Rogue wear leather because leather makes the lest amount of noise when you move. cloth shuffles and metal armours all clank and scrape. some things my not makes sense but it is common sense people.