I'm not sure that confused passengers comes purely down to stupidity. As a frequent flier it is easy to forget how frightening travelling maybe to some people who rarely leave their own house. If you spend a few moments in Heathrow or Schiphol to watch people desperately scanning the boards and searching for gates amongst the shops and hoping that the someone will guide them onto the plane which they may have just spent their life savings on to travel. Some will have emotional stresses, others will be tired.
But even as a frequent flier, we all have a preference of which airport to transfer through 'because its easier'. Thats a choice you make because your familiar with it and feel comfortable there (I personally prefer KLM via Schiphol as the UK and International flights are within the same terminal).
So what i'm saying is that, people boarding a wrong plane, or concerned about where they are going to sit because they don't understand the seats rows maybe just because this is a completely brand new or rare experience for them.