Yes, that's true. The brand of marker, and even the color of marker makes a big difference. Expo blue and green seem safest, with red distinctly unsafe. And burn in is real, though you can often get stuff clean with a decent vinegar based solution...but who wants to do that?

That's why the whiteboard repair fluid stuff sounds interesting. The only good options I've found for eraseability are a good expensive whiteboard (and even then you takes your chances) or glass (which you can paint the flip side of or put over wood, etc for aesthetics -- but it gets heavy and expensive, and I guess sort of dangerous, at large sizes).