I think drivers are the thing they change the most, along with putters.
They seem to bring a new one out every year that adds 20-30 yards, that's the difference between going for a par 5 in 2 and having to lay up, going into a par 4 with a shorter iron etc.. If you don't move with the times, you get left behind.
As others have mentioned with the putter, it's all about confidence really. Sometimes you want to look down and see a blade behind the ball, sometimes your eye needs to see a bigger mallet kind of putter to give you the confidence.