The POD states that the second arg is:

$appname -- full path name of executable module

So you'll need an actual executable program there, e.g. perl.exe, which I guess is found in the $^X variable (the current Perl script is in $0).

So, why does system() work? Because the system() call is smarter and will try to start the main application if you have the file extension associated with something. And .pl is associated with perl.exe if you use ActivePerl.

/J