I wonder how long it will take for them to phase out the KC-135's. The Wikipedia article claims that Air Force studies say the KC-135 could be viable until 2040, although with increasing maintenance costs. Apparently the KC-10 is expected to remain in service until 2043. These A/C don't see nearly the usage as their commercial counterparts though do they?
Which is why I don't understand why the airlines can't still be taking delivery on new ones. Regardless of what major airline you are talking about/to, they all seem to be bemoaning the lack of a good replacement for the 757 and the 767.