Not having flown a heli with an APU maybe I am biased, but in the examples you give the blade deicing on a 225 continues to work on one alternator (they are big alternators) and you can press both start buttons at the same time, although I grant you that starting will then take place consecuitively not concurrently due to the limitations of the DC supply system. Airstart means the APU must be working, otherwise your bird is dead - ie a single point failure. A few plusses and minuses there but when you include the additional weight and maintenance of what is effectively a third engine, I'm not sure the case for APU is clear cut. Of course if you want to run your aircon before startup, APU is great and that's why EC offer it as an option for VIP / hot weather (not usually a problem in Aberdeen!)