Originally Posted by
Stucky
Because it's lighter than steel; but more cushy than Ti. for a sensitive thing like a fork, which accounts for a good deal of how a bike rides and how much vibration and nastiness from the road it transmits. The bike-shop dude knows this...he just assumed that you don't.
On that theme, it helps explain the existence of other bikes with a bit more CF in the tubes coming from the wheels, but with Ti tubing elsewhere.