Barnaby, I think that because it was an accident (even due to negligence) that is exactly why the "doctor" reflex kicked in.
They knew--or at least Gerry and some of them realized--that an accidental death would not be a simple matter of accident. They could very well lose the twins, and so they were desperate.
I just think that they were so caught up in the fear of losing the twins also that they did this. Particularly if, worst case scenario, Maddie fell and in coming home after a night out, they didn't even notice she wasn't in her bed.
Some professions seem to be a part of one's personality as well. I don't know any doctors that well, but I know from living with a civil engineer that the "engineer mindset" never really goes away. And my family tells me that I get a most annoying "teacher tone" to my voice and body language at times! I think it's plausible that at a time of crisis, the doctor training simply took over, in an automatic reflex. The same kind of brain that is able to think clearly during a cardiac arrest could function, under a perceived need, just as well to "save" his family.
Remember every positive word about moving on is/was about the twins. They have to keep reminding themselves of that.
That's why the words of Kate's diary ring both true and false. She really does miss Madeleine but she also knows Maddie is gone.
