it doesn't, if that were allowed it would create ambiguity since '*' is a valid character in a variable name. see:
//var %c_ = 3 | echo -a $calc(%c_ * 2) - $calc(%c_* 2) - $calc($null 2)
%c_* is quite clearly being treated as $null there since, presumably, a variable named %c_* doesn't exist.
chacha: there's also
/filter -wlfc # tmpfile which, since we're already straying from the original script by omitting the (<nick> != $me) check, will include the status prefix of each nickname (@%+ etc.) if there is one to include. it saves us having to resort to such measures as a $regsubex() loop which are all but overused these days :P
there's also the possibly of receiving a
* Line too long: $regsubex error with a suitably massive nicklist