What a player might be observing is a form of
the confirmation bias. A good example of this is that many people believe that
there are more emergency room visits during a full moon then on any other day. The only evidence for this comes anecdotally from nurses and doctors. They are more likely to remember and report a surge in patients on a night with a full moon than any other night. Thus, it may seem like the full moon causes people to go a little crazy. Statistics do not lie and it can be shown that there is
no increase in emergency room traffic on nights with a full moon. This equates to the situation in Guild Wars 2 where you have, firstly, players only noticing when they are not getting good loot, and secondly, only players getting bad loot are reporting their problems. Thus, it may seems like there is a problem when in fact one does not exist.
The other thing that may be a factor here is that people
are terrible judges of true randomness. As an example take the following two images. Which do you think was generated by the most random process?
It turns out that the image on the left was generated by simply placing 100 random stars with in the fixed area using a random number generator. The image on the right was generated by first dividing the entire area into 100 squares and then randomly placing a star inside each of those squares. See for yourself in the image below. No two stars are in the same box.
It is hard for a lot of people to accept that the image with the black stars is in fact generated by a more random process than the image with the blue stars. This has a lot to do with how
the human brain is constantly looking for patterns. When the brain sees these patterns it attempts to correlate them to a cause even if a cause does not exist. Essentially, this is the illusion of luck. It is why people can believe that they are on a "hot streak" or why they might believe an object gives them an increased chance at success. Some call this
the Gambler's fallacy. In the end it is all the same thing. People are terrible judges of randomness. That is why we invented statistics.
So, what does this have to do with Guild Wars 2? Imagine your character is walking around in the image with the black stars above. Each time it encounters a star you can equate that to "getting good loot". Now if your character was in an area of that image with a clump of stars before the November patch then afterwards you managed to find yourself in a void you might say to yourself, "Hey, I am getting less loot after then November patch then I was before. The patch must have changed something." This is a perfectly reasonable hypothesis, especially if you think the world looks like the image with the blue stars. This hypothesis has been shot down by Arena Net who have looked at the bigger picture. They can see the entire image and use statistical techniques to determine the randomness of the spread of stars. Unfortunately, as players all we can see is what is around us. Thus, in the end I am going to trust Arena Net when they say that there is no difference pre and post patch.