Apparently people don't understand statistics and the actual definition of random.
Your evidence is anecdotal at best. Get a larger sample size and report back to us. It is well within the realm of possibility that you wouldn't get any loot in an instance run.
To help the point, let's say each boss has 1 piece of gear you need out of... 5 possible drops. So a boss has an 80% to drop nothing you'd want. That can happen 6 times in a row fairly often.
There is NO way to tell from your sample size if the loot tables are buggy. If you really feel that this is something that should be checked I will gladly send you a PM with a list of drops from each boss when I run the Hammer. If you can get some more people to do the same you'll have your experiment.