I beleive that ignoring holidays and birthdays etc. also hides/masks the passage of time from the JW rank and file. When people put significant planning into a special event day (like a birthday), it further punctuates that arrival of that day and makes the passage of time more apparent.
The Witnesses are encouraged to live each day the same as the last -- this disconnects them from the passage of time and further hides the errors and changes of the JW teachings.
As a kid we has regular family celebrations until I was 5 or 6. Then my parents got the "Truth".. We no longer spent any time with my grandparents or extended relatives on holidays etc.