A. I've noticed this myself over the years, but only on occasion, not as frequently as you seem to have experienced. I also remember asking about this phemomenon to a very highly-respected master blender a few years ago.
What happens is, sometimes a little ammoniac works its way into the end of the foot during the aging process, which is where the bitterness comes from. Once it burns-off, the cigar rounds out.
The only thing I can think of that would cause every cigar you reach for to taste bitter would be that you have a lot of cigars that were not fermented properly. (See also: "Funny odor in humidor.") | 
