Personally, I don't agree with that. Yes, foundation is supposed to be the same colour as your skin and blend, but missing your whole forehead could be obvious. Even if someone has full bangs or always wears them down, they occasionally sweep to the side and as someone mentioned, there is always the wind.
Sometimes, I just think some makeup artists try to give unheard of advice to magazines so they seem uber creative.
I have never had an issue with breakouts/makeup and bangs. The only issue I have is when it gets super hot and humid out. Then my makeup can mix with humidity and sweat and transfer to my bangs. When that happens, I just apply Blot Powder to my forehead and my bangs (it works just like the dry shampoos currrently flooding the market).