Brilliant post, Terry. Well articulated ! Now, to attempt to answer your question as to the cause(s) behind the changes, my thoughts are captured in one word, "exigencies" !
And to dropoffyourkeylee :"I have always had the suspicion that the no-Christmas, no_Thanksgiving, prohibitions were to create a rift between the family members who stayed with the WT and those who went with the 'evil slave' of the time, the various Bible Students movements. I grew up in the Chicago area in the '60's and even at that time there were family members of the living JWs who were in the other movements."
I must admit that I never reasoned along that line until now, Now, it sounds quite plausible, especially when you consider these changes as the "first baby steps" towards adopting excommunication or disfellowshipping as an instrument for enforcing adherence and group cohesion.
My take, previously, on the no-Christmas, no-birthday, no-blood and all the other no-nos was that they served to set the organisation apart from mainstream churches and create a hoo-hah that kept the organisation in the headlines ! Let's face it, if the organisation didn't have a catalogue of no-nos, they would simply have greyed out and their members absorbed into mainstream churches. Hence, it's all exigency, exigency, exigency ! going back to Terry's question.
This penchant for controversy has certainly worked well for the organisation !