Actually, it's not specifically the linkage; it's really that 3.16
states that it is undefined whenever you do things that are not
*explicitly* defined.  Since no definition is offered for what happens
if main is declared with a return type other than int, doing so
invokes undefined behavior, with precisely the same implications as
doing so in a way (like referencing an uninitialized pointer) which
is specifically stated to invoke undefined behavior.

Point taken, though.  I was mostly just putting that in to avoid the
initial stream of "but I saw in a book that ...", and make people
double check.  :)

-s