You've just given examples where a great UX has made up for any apparent UI-deficiencies. SDK buttons are "good enough," in that they're UI elements that won't

You've just given examples where a great UX has made up for any apparent UI-deficiencies. SDK buttons are "good enough," in that they're UI elements that won't negatively impact UX on their own (implementation obviously matters here). "Good enough" is all you need when you have a superior UX.