Diablo – What armor and weapons do Crusaders use

There are no real "tiers" of equipment. Instead there are rough groups of armor that match visually.

If all of your items are from that given group, they will match. However, this does not determine their stats.

From Blizzard Community Manager Bashiok:

We separate out 'item tiers' for their visual appearance first and foremost. We have a number of "armor sets" (18?) in the game that match visually, and so we call them 'tiers' because there's no real better way to say it. When all of your items are from that 'tier', you'll match. That doesn't directly determine their stats, though.

They're spread out in a logical progression, and items get more awesome looking as you go further in the game. Ipso facto the higher the visual tier the better chance it's a more powerful item, but it doesn't preclude the possibility of it being worse. You can absolutely find an item from a visual tier back in Hell difficulty that's better than an item using a later visual tier in Inferno.

It's best to just expunge the term 'tier' from your minds, because it really has nothing to do with any kind of stair step or item upgrade approach. It's just models and textures.

After reaching level 10 your items will lose 10% of max durability with each death,items will also lose durability during combat,and not just by taking damage also by dealing it(with every successful spell/attack),also just by attacking other parts of your gear will still suffer durability.

Note that durability is lost very slowly,probably increased with levels of gear/enemies.

Not sure why people say items don't suffer durability,i can't seem to find any durability changes in changelog also on diablo 3 forum someone confirmed durability loss(5 hours ago).

It might be bugged or unbalanced but rest assured it will be implemented since durability system is very good way for players to spend their money and blizzard knows it.