+1
I may be alone on this, but I think aircraft footprint is a big issue as well. Yeah, the bus might be able to offload 200k and carry 75k of cargo, but there is only so much ramp space at deployed locations and # of tails matters. I can't count how many times I have been haulin butt across OIF/OEF, trying to be 5 places at once. Not saying the Boeing is better because it is smaller - I don't have the #'s handy, but there is more to the equation than amount of gas/cargo one tanker can carry. Bottom line - When it comes to fighting wars, I'd rather have 20 Boeing's than 15 Busses at a forward location. Now routine AMC missions... that's another story...
The 135 is still going very strong, and will continue to be a reliable platform for some time, but you can only fly it so long before the wings start comin off. I just wish they could open the production line again!