I never noticed a difference. I'll have to look for that next time.

True they do sound the same. But, there is a distinctive difference when Derek sings I can tell that there is another singing in the other two films. I like them all. But, there is something about the way Howard McGillin sings that sounds like something worth remembering. It sounds deeper and everything else.
It took me awhile to come up with a reason why I prefer Howard's voice talent over the other two.