Well if you're going to copy from some place, you can't really go wrong with Tolkien when it comes to a fantasy setting... and besides, they had no problem copying Marvel Comics by including adamantium.
Well it means some one wasn't really thinking things through. With no real restrictions there are so many interesting things to make armour out, take Feathers or Porcelain for example. Now this is just my personal idea but I get the impression they didn't do the thing where they lock the artists in a room and only let them out until they've come up with a coherent vision of Cyrodiil.
So instead we get a mix of Tolkeen and old stuff, mostly old stuff actually since Mithril has been around for a while.
The reason I asked is that I'm working on a mod that overhauls weapons and armor, and it involves making separate leveled lists for imports... so I realized I didn't know whether or not mithril armor belonged in the import list or not...
I bet elven armor is also made from mithril - it's just mithril banded mail as opposed to mithril chainmail...
Just about everything is import, did you see all the derelict mines in Cyrodiil.
Slightly more serious:
Elvish mithril and Argonian silver, crumble I can.
But first, I improve all created by man.
I devour all things,
Bird and beast, serfs and kings.
Though my pace is even, men curse my speed,
Wishing I were lazier in their hour of need.
I can creep and crawl, or rush, even fly.
I am all thou hast.
Tell me, who am I? - http://www.imperial-library.info/riddles.shtml
Light armor is made from fur, leather, chainmail, mithril, elven or glass. This is also the order of their quality and expense, fur being the least protective and cheapest, and glass the best and most expensive. Fur, leather armor, and chainmail are readily available throughout the empire. Mithril, elven and glass are exceedingly rare and are only found in ancient ruins and remote tombs. - http://www.imperial-library.info/obbooks/manual_armor.shtml
Never thought I'd reference this one.