Why does ImageButton.onSetAlpha() return false always?

I was looking at this post to figure out the differences between a clickable image view and an image button.

In accepted answer @Michael says:

EDIT: Also, ImageButton.onSetAlpha() method always returns false, scaleType is set to center and it's always inflated as focusable.

My question is: Why does ImageButton.onSetAlpha() always return false? I've checked out the docs which says that the default implementation is false, but never explictly says that onSetAlpha will always return false.

Thanks!