lol hixxy :*
$calc() also does things like evaluate variables/identifiers in cases such as $calc(1+$x), then there's $calc(0^-1) to worry about and such ;P
as starbucks said, detecting division by 0 involves almost exactly the same amount of work as re-creating $calc() using basic mathematical operations.. such as those offered in /set, which is no easy task! that's why i laughed at Riamus2's suggestion