Governing Body 2.0 got together, and one of them wrinkled their nose and said "I never understood why we called it the Memorial...."
2 years and 9 other meetings later, this GB member got his wish, and now on the invite, it says "anniversary".
It's good to see that GB 2.0 is at it again, revolutionizing JW's with their awesome insights into semantical meanings.
(disclaimer: the above is a hypothesis of mine, but I bet I am not that far off)