You have it backward, Amazon and Samsung's own appstores are desperate attempts to get enough traction out of Play Store so that they are not forced to succumb to Google's demands. The issue here isn't Android not being open (which it is), the problem is Google having a lot of control (including full veto power) on devices shipping with Google Play Services, while making them an increasingly necessary part of Android. You can make an Android device without having to let Big G call the shots, but they're banking on you NOT doing that because no one wants a phone without the Play Store and its related services.