There's a historic reason for that that predates me. I think it was the case that originally just the TextBox had the HideKeyboard block, but other components eventually had the ability to obtain keyboard focus so it just made sense to have the ability to hide the keyboard from anywhere on the Screen regardless what components were available.
That said, the blocks really should have the same outcome so the fact that they behave differently needs to be addressed.
Edit: In particular, older Android phones used to have a trackball that could be used to navigate the UI, so things like Buttons could be focused even if the screen wasn't touched. This is also why Button has GotFocus/LostFocus even though these days it's very difficult to focus a button.