Originally Posted by Cassadamius
No, it is as opposed to weight. The larger tubes weigh more. Cervelo has just mastered the ability to keep them light, so they make the Soloist. If the weight was equal, then most road bikes would be aero. And as far as cheaper and easier to design, check out Cervelo's R3 - squoval tubing (seemingly as complex if not more than the more standard tubes of the soloist) and frameset costs $2800.
That idea USED to be true. The modern tri bikes are every bit as light as their road bike cousins. Prodir's TT bike in the TDF hit the UCI weight minimum. My Kestrel tri bike is the lightest thing in my stable.