Though I'm no expert, I believe they use carbon fiber for its excellent tensile strength and low density.
Carbon's covalent bonds are very strong. The most evenly distributed bonds are as in diamond. With graphite, carbon is making more directional bonds in the form of planes, or sheets of graphite. However, I believe Arthur C. Clarke conjectured that a space elevator could be created with a few inch (or other small unit) diameter rope of "carbon fiber". I think what they're saying this incredibly strong rope is the same kind of carbon structure as in carbon nanotubes. Yet they're still able to make a crude version that is not exactly the same structure and strength as carbon nanotubes, but is somewhere in the middle. And that's what I think they're using in car hoods, bikes, and these compressed air tanks. Not quite nanotubes, but exploiting the same strength of carbon using different structures.