OEM paint loss in rain rails- is this normal?

Let me start by saying that I have always assumed that my car had factory paint on it....I have owned the car since I was in high school (in the 1990s) and this issue has been there as long as I have had the car but just recently, it occurred to me that I shouldn't take it for granted.

On each side of the car, the paint behind the bright work (inside the "rain gutters") has worn away, revealing a white surface. I was told many years ago that this was primer or some other material that was used in the original manufacturing...

Has anyone else seen this? It would be an awfully odd application of bondo if that was the case.

Sorry for the crappy pic... the rest of the paint on the car (aside from needing a wash/wax) is in decent "20 footer" condition. Fortunately, you can't see this unless you're close to the car, looking down. :)

Thanks for any input!