Back when Android had a light statusbar (pre-3.0) it was an issue because the statusbar was always there, always in the same position as long as the screen was turned on. This is most likely why they've changed it to a dark one since then. I haven't noticed any burn-in on my 2 year old Note 3 either and I will agree it probably isn't an issue under most normal usage, but in specific cases (that are still very much normal usage) like the one I just mentioned, it can be.I've been using Samsung Galaxy S mobile phone family since my first smartphone. I also own a PSV. Neither of the screens has signs of burn-in.
For that to happen you have to leave a static screen for days. Normal usage won't damage the screen at all.
Edit: For the record, I have a friend who got burn-in as a result of the light statusbar on early Android versions so I know it happens.