That makes me wonder why there isn't a Learning Perl for Unix, or something like that.

Actually, I think it's a good idea to favor non-platform-specific texts, but that makes me want to again question the Win32 version's existence. Shouldn't "we" be teaching Perl, and maybe offering a "next book" that touches on Win32-specific matters and assumes a basic understanding of Perl already, instead of teaching a Win32-specific dialect of Perl?