Linen is actually a pretty incredible fabric. I learned a little bit about it when I was in Europe and took a tour of a flax farm.
It is expensive because it's quite difficult to make. It takes a lot of work to get from the plant to the fabric, unlike, say cotton, which is relatively simple to make.
Linen is much stronger than cotton, even if it does have a tendency to break if it gets creased too much in one place.
It can also hold a lot of water before it starts feeling damp (which is something to be aware of if you have a linen suit). It's even stronger when it gets wet than when it is dry.
Whew, I'm starting to sound like the guy who told me all this trivia. He was a goldmine of information about linen, maybe because he wanted to sell me some linen suit jackets or something.