I think it is more to do with the emergency generator as the APU does not supply hydraulic power. The RAT can provide power through the emergency generator by pressure in the green system but under 260kts this is very minimal. With the APU out on a 330 you still have three generators and all hydraulics. The issue of ground services in FCO is not a factor. If it was either hot bus 1 or hot bus 2 INOP also I honestly can't see why that would make going with the APU INOP any worse as the only things these do is connect to either battery 1 or 2. 1 battery is just as useless as 2 if that is the only power you have in an A330. There will be more to this story than we know.