One other thing to remember is that CO just doesn't have that many wide-bodied aircraft to begin with, unlike UA or AA. CO would rather put their wide-bodies on more profitable/lucrative routes: international ones. Even so, CO still can't run a non-stop IAH-FRA, when LH has been making butt-loads of cash off that route, since no-one else competes with them. CO just has a "direct" flight, stopping in EWR, with a AC change! Only the flight number stays the same. I've flown CO 51, and the plane I was on was going to Spain or Portugal, NOT continuing onto FRA.

A related question: How are the loads on UA's widebody transcons?