Colin Johanson has just made a post on the official forums updating the community about the loot/drop investigation.
Since the community was still reporting issues with the drops they were getting, ArenaNet took another look at the issue. It appears they found the problem:
The rules by which you qualify for credit for an event or for experience when killing a mob are different rules than those used to help determine if you qualify for loot. Some of these were set up to be unintentionally restrictive, and as such you could kill a creature with a lot of health (this was most noticeable on champions) and not qualify for loot, despite qualifying for all other credit.
Once fixed, all champion mobs will correctly always drop 1 blue or better loot item, and all veterans will have a chance of dropping loot better than regular mobs as outlined in the November release. Please note, it is still possible to kill a creature and not do enough damage to qualify for loot (which is the only way you won’t get loot for a champion), it is also still possible for veterans to not drop loot at all, since they simply have better odds of dropping loot than normal creatures but no guaranteed drops.
He goes on to say that they will repair the issue with the February patch drops and not only that, but they plan to make specific areas more rewarding for the players. We'll see more information when the February patch notes are published.