s/// returns the number of substitutions made, so that's what that map block is returning. Although it's generally not considered good practice to modify the original list by modifying or assigning to $_ in a map block, the first version could be written as map { $_ = quotemeta($_) . '$'; s/\\\*/.*/g; $_ } to achieve the desired result. Alternatively, as of Perl 5.14, you can say s///r to have the regex return the modified string, e.g. map { my $x = quotemeta($_) . '$'; $x =~ s/\\\*/.*/gr }.
Update: Note that your second regex includes /g, while your first one does not; I've added it to both my examples.
Update 2: Or even just map { quotemeta($_).'$' =~ s/\\\*/.*/gr } or map { "\Q$_\E\$" =~ s/\\\*/.*/gr }
