It's not a huge surprise. Farmville and it's ilk were always terribly dull games. People weren't staying for the gameplay, they were staying thanks to the social pressure of all their friends playing it too (and having to log in to help them advance).
... and I hoped it was peoples common sense kicking in, but apparently it's just the fact that now with the notifications gone, people forget about their game. That too speaks volumes about the majority of the players.