Samsung has a skin on it, it's minimal, but it's still there.

I have a dozen nonstock app installed... and they all fit with the style just fine or perfectly.

>It's confusing enough just knowing when to use the hardware "back" button or not.

I've never understood and may never understand this confusion though I hear it and try to address it constantly. It's the same in almost every app and is different in only a very few apps where the overridden behavior makes a lot of sense.