Android comes with virtually no restrictions, and that can seriously hamper the user experience. Why? Because left to their own devices (excuse the pun), each individual manufacturer only has their own company’s gain in mind, along with hopefully the user’s overall experience. But clearly, none of them have their competitors’ customers in mind, as evidenced by the disparate button placement on Android (not even getting into the huge problems caused by there being more than one button anyway, but that’s for a later post).
Android isn’t “open” for the sake of being open; it’s open so more manufacturers adopt it.