The very fact that people always refer to Dick's is part of what makes it seem like it's just his special thing. I think there's even a story--is it maybe Devin Grayson?--where I swear Bruce pretty much suggests he made it up because Dick needed it. Which makes sense. Dick was a little boy and took it really seriously. It gave him direction. The other ones all had very different ways into the group where it didn't mean the same thing so it wasn't necessarily. (I know it was Devin Grayson who had Bruce say that Dick practiced the thing for a week and seemed to grow taller every time he said it to himself.)