Probably won't make the OP feel any better, but for what its worth, it took me close to 30 times in Nightmare to get my sha touched mace. Got it the week before 5.2. It's very easy to despair when you've run the same thing so many times and don't get what you need (only what you already have - I must have gotten about 5 tier chest pieces). It's very discouraging.
Probably the worst is that it's off the last boss. It would be bearable if it was off the 1st or 2nd, but no... the last one, which means you have to endure bad groups for the entire run. And if you run it multiple times per week (I usually did at least 3-4), you begin to lose faith in anything. Heck, I remember getting so punchy and irritated on more than one occasions that I would vote kick people for the smallest infraction (never worked though).
For me the real "kick to the nads" so to speak was two or three weeks before I FINALLY got the weapon, I did Sha with some friends, and the mount dropped for me. As excited as I was over a very rare mount drop, I was infuriated that the evil RNG Gods would choose NOW to favor me, rather than with the thing that I really needed and wanted. Figuring my luck had changed, I immediately ran 3-4 Nightmares with my most tolerant friend, and nothing. I lost hope, and literally gave up for those two to three weeks and ran absolutely nothing. The following week, my friend dragged me along, as I didn't want to go, and it dropped. Though the group had been a good one, we just about wiped at 1%, it was a miracle that they got her down (I had already died 3 times by then).
So, OP, I know your pain, and all I can say is hang in there... it may be the day before the next expansion when you get it, but you'll get it eventually. Hopefully Blizzard comes up with something better than "significantly increased" chance... when I read it, I laughed. Maybe now they mean it'll only take 25 times instead of 30 /rolleyes.
I do like some of the suggestions here, in particular the pet-battle-trap esque one with an increased percentage at a drop for every time you don't get something. Anything that would make life better for us "outliers."
Edited by Aelena on 3/9/2013 8:14 AM PST