When it all adds up, I think people would rather the superior defensive capabilities of heavy armour than the inferior capabilties of light just so they can move faster, sprint for longer and have more inventory space (though at a moderate level, I think, there is a heavy armour perk which reduces the weight of heavy armour).
Assassins and thieves are basically the same thing. When I was referring to thieves, I was also talking about assassins.
Yes, armour is important for them when they can't kill something in one hit. Which is why I use Nightingale, as it has a superior defensive rating when compared to glass (and also gives me some nice thief perks, like increased pickpocketing).
My argument about armour values is not redundant. With the right enchantments, you could craft steel and elven armour to that level, but if you had Daedric, you could enchant it to increase things other than defense.
Edit: Found this on a Skyrim Wiki
So why then would a thief use Destruction magic?Skills should synergize—they need to work well together and complement each other. For example, combining Archery and Destruction may not be the best approach: both do essentially the same thing, staggering and killing things at range, so they're often redundant, and you can only use one or the other at any given time. Meanwhile, Archery prefers a high Stamina, while Destruction requires massive amounts of Magicka. Whichever of the two attributes you increase during a level, the skill depending on the other will soon suffer.
I also found another quote from the same page.
Stealth means no magic without the quiet casting perk.
On an unrelated topic, I think the best racial power is definitely the Orc's Berserker Rage. Seriously, you take half damage while dealing double? That's some serious ownage right there.
An Orc in Daedric, wielding a Daedric Battleaxe while using Berserker Rage... O_O
I pity any who come upon such an over-powered character.
Oh, but unfortunately it doesn't work against magic. Luckily most enemies don't use magic, though.