StarTrekAngel - I agree with your theory that the birthday ban was put in place so that the money meant for birthdays would be freed up for "donations" to the Tower. I have thought that for years but have never done the math on it.
Birthdays and Xmas were both celebrated at one time in the Tower religion - the old Golden Age magazines used to advertise Studies in Scriptures as a gift suggestion for Xmas. I am not sure about the birthdays but I believe that the birthday ban was put in post-WW2.
Regardless, I do think that money was the originating factor - the control and keeping the JWs 'separate from the world" are only the results that are actually seen - the money is the primary reason.
Hell, the Tower doesn't even want the kids to buy ice cream - how the hell could they ever have a birthday party without ice cream??