KenV, do you mean too highly optimized for pax carriage? I had heard that 777's carry a bit of cargo as well ... but the devil is in the details.
Well, 777F is a good freighter and a straight passenger A330 can be made into a tanker. So a freighter door and floor is not my point. I understand (but cannot confirm) that the 777's structure is so highly optimized that adding things like a refueling boom in the tail, fuel bladders in the lower hold, and WARP hardpoints and associated plumbing/wiring would require highly costly redesign/modification. And finally, it would be essentially impossible to harden the FBW flight controls on the 777.
The 767 design was less optimized and had manual fight controls. The A330 design was basically a stretched A300 with new wings and an A320 FBW added on. That A300 fuselage is why the A330 sits nose low on the ground, it has the same nose gear installation as A300 (albeit strengthened) while the main gear are taller which was possible given the new wing. I have no idea how Airbus proposed to harden the FBW system in their A330, assuming they even tried. Since Airbus was willing to propose an airframe with no cargo door and no freight floor contrary to USAF's spec requirement, perhaps they did not include FBW hardening either. I have no idea.