Very good point jb. Some of the older ones in the congregations may remember the "Daily Manna and Birthday Record". This was the predecessor of the "Examining the Scriptures Daily" book. I was told that you had to make a note of everyone in your congregation's birthday, and you had to give them a card. The brothers and sisters in a big congregation would have to buy cards pretty much on a weekly basis, and so some of them were quite relieved when the birthday ban came, because it was an expensive business! I wonder if this was the true reason for the axe, i.e. plain stinginess?!
I have never heard of one satisfactory reason for the birthday ban coupled with the wedding anniversary obsession other than the insidious reason you mention. To me they are the same thing.