Actually, you can -- it's not that elementary, but you can build tons of things out of just glass...nothing else. A few layers of Knytex with the appropriate resin will be extrememly strong.

You can make a sub enclosure using 'glass that is only 1/8-1/4" thick if you design it properly (depending on the application of course).

I don't know if you have ever designed or worked with composites before, but you could make a box out of 90% fiberglass if you wanted to, and it would be extrememly light and you could use it as a jackstand.

Composites are a trade off in many aspects, but the main advantage is it's strength to weigth ratio....why do you think carbon fiber is so popular?!?