How do they not break? It's frickin glass!

Those two-man submarines these days dive in the deepest waters, and they do have glass windows. Some metals would break, but glass is quite solid, if we are not talking about thin bottles.
And aswell you do have bulletproof glass today.

Well I believe that glass in Skyrim isn't awesome and solid as it is today, but after all, it surely can take some hits. And it is light armor, which puts it in the same "school" with hide and leather. Nothing very protective anyway if it was real.

Correct me if I'm wrong but glass swords aren't really made out of glass are they? I remember reading a book where it said that it was made from some sort of material but not glass that's from windows.

There's two different kinds of glass in Skyrim.
1. Windowpane like glass
2. Malachite Glass

Light armor forging book says there is a difference between the armor glass and the window glass.

"What we call Glass is nothing like the window panes you see in houses. The greenish material is far stronger and has a much higher melting point."
http://www.uesp.net/wiki/Skyrim:Light_Armor_Forging

As far as the game goes it's not really glass. It's some type of volcanic mineral that has the appearance of glass but is far stronger. It's only called glass because it is somewhat transparent.

Same as metals, there are different types of glass. And honestly, I'd dare anyone to try to break 1.5 inch solid glass cube. Like I said above, glass material we find in bottles or windows is completely thinner and different type of glass.

Not windowpane glass. This is malachite glass, one of the toughest materials in all of Nirn.

It's not made out of real glass, it just looks like it. It's made out of Refined Moonstone and Refined Malachite. In Morrowind and Skyrim you have glass mines. Which means this material is mined not heated up from sand.

http://en.wikipedia.org/wiki/Obsidian

MALACHITE GLASS IS NOT NORMAL GLASS! please read some books about that or go to UESPWiki to learn more about it (dont mean to offend)

Hello, glass. Meet hammer.

Of course, then you get the instacooled glass teardrops that are virtually indestructible on the bulb but lightly tapping the tail makes them explode.

But yeah, as people are darting around, the "glass" weapon are made of a green mineral called Malachite that, while naturally brittle, is fairly hard and can be given a really nasty edge. Presumably, since it's the equivalent of ebony/daedric forging, it takes supernaturally high talent in smithing to actually craft it into the durable armour and fluted swords you see made of it, which probably overcomes its brittleness by some process (melting it down?) as well.

http://en.wikipedia.org/wiki/Malachite So, it's not actually glass at all. That's just the colloquial name, I guess.