why not #include "config.h"?

[Steffen Dettmer]

I hope I don't ask a FAQ. If so, an URL would be appreciated.

I've read here that someone could (should?) write
  #include <config.h>
specifying a system header instead of the IMHO correct
  #include "config.h"

As far as I know the difference is that in the first version
system directories are searched but user directories in the
second.

Is this a kind of trick for something?
Is is guaranteed that all compilers search the user path after
the system path if the file was not found?

oki,

Steffen