Its my understanding that the 2004 models require you to push the button while the 2005 models do not.

I checked again with the service manager (wanted to make sure I was not screwing up my top) and he said a few things were changed between the two years and he believes this to be one of them, as the 2005 models he has driven and shown to buyers do not require two hands.

Which explains why some of us have to use the button while some of us do not.