villas,
I completely get everything you say however it's not the technical operating matters I'm talking about but more related to the prep/organisational aspects of the day (I have edited my post to clarify). My previous airline has over 25 years experience with the A320 series and I guess over time felt the need to condense and simplify certain tasks or simply allow for flexibility.
You say Airbus, being the manufacturer and having access to all the data, clearly should not be ignored because they know what they're talking about. However, I'd like to play devils advocate for a minute and ask the question: Do Airbus fly their planes on a daily basis with real world operational constraints (time being the primary one)? Were the procedures written with 10 interruptions by cabin crew, handling agents or ATC? No Airline operates within a sterile vacuum, therefore overtime adapts procedures to suit a typical day. Aviation doesn't care if you fly Airbus, Boeing or Embraer!
It might be a crude example, but just consider this one for a second. The Oxygen Mask test appears towards the end of the Cockpit Prep tasks (when both pilots are seated). The amount of things pilots must do before they get to the lateral console and glare-shield setup in the real world is simply crazy. We currently do manual loads sheets and have countless interruptions before we get to the briefing. Often there's 3 minutes to go prior to push back (fully loaded A321). Now the Engineer is connected and before we check the masks we need to ask the engineer to temporarily disconnect/remove his headset. What I'm saying is the preparatory tasks as specified by Airbus assume a text book day out. Flexibility can be a bad and a beautiful thing. I should be allowed to get the Oxygen test out of the way when I arrive into the flight deck. Some might say you just take the common sense approach to things, I agree... but when your common sense is questioned because "it's not in the book" you begin to wonder.
Don't get me wrong, we need a standard set of procedures. We need a starting point after all but to forcefully "follow the book" in the precise order it's written when the world around you makes it difficult is IMHO stupid. The glove no longer fits, but we keep forcing it on.