I enjoyed that Peter.
One thing I have always wondered is why do they not use the tugs to take the aircraft to the end of the runways, this would save a phenomenal amount of jet fuel, engines coule be run-up prior to reaching the end of the runway and a parking area to go to should there be a problem.
When I worked for British Airports a study was done to look at that idea.
It was decided that it was a non-starter, but I cannot remember why.
Thinking about it now I can visualise several reasons:-
Tugs are expensive and there would have to be many additional ones bought to implement the system - maybe the capital cost, plus the operating cost including tug drivers' wages and training would be more than the taxiing cost of fuel.
A ground engineer would have to accompany the tug to the start-up point to monitor the start-up. An expensive use of highly trained personnel.
The sequencing of take-offs is not always the same as for taxi clearance, because of en-route ATC, so tugs and engineers would be tied up waiting for clearance.
The 'Holding Point' would have to be much larger to accomodate several aircraft for the several minutes it takes to start 2/4 engines and do the after-start checks before the ground engineer is instructed to disconnect the truck and that is done and the steering pins relocated.
ATC would not have the ability to to give a clearance to an aircraft approaching the runway to enter the runway and 'take it on the roll', i.e. not stop before take-off.
As you see the decision is more complex than saving a bit of fuel.
On the positive side I have been on several flights recently when only one engine is started up on push-back and the second one while taxiing to the runway - preferably before being cleared for take-off