So, Arthur's Wizard, as you probably see from the other follow-ups to my post, saying "My aircraft has an APU" really is just an insider way of saying "Mine is bigger than yours". Aircraft of course, although possibly also other equipment.
There are many other similar comparisons, where a practical limitation is turned into a positive feature, the most obvious being the number of engines. I might need to put on my flame-proof suit before saying this, but for example pilots of three-engined aircraft will claim that three engines are better, when in fact from an engineering and commercial point of view the only reason you would ever add the third engine is because you couldn't pass the certification OEI requirements with only two. That's not to say that you can't then put a positive spin on having three (ETOPS anyone?) but you only started down that path to solve a problem. Thus, the APU chaps can drink coffee and preheat the cabin, which is a nice touch, but they started down that path because of the technical problem of starting a large engine.
And for apruneuk:
We can preheat or precool the cabin too, but we just start an engine as our "APU". When the passengers arrive we start the other APU and take off!
