They are usually converted into shell scripts, not just copied.

Unix: (.pl removed)

#!/path/to/perl/used/to/install/bin/perl

eval 'exec /path/to/perl/used/to/install/bin/perl -w -S $0 ${1+"$@"}'
    if 0; # not running under some shell
...[ script contents here ]...
[download]

Windows: (.pl ⇒ .bat)

@rem = '--*-Perl-*--
@echo off
if "%OS%" == "Windows_NT" goto WinNT
perl -x -S "%0" %1 %2 %3 %4 %5 %6 %7 %8 %9
goto endofperl
:WinNT
perl -x -S %0 %*
if NOT "%COMSPEC%" == "%SystemRoot%\system32\cmd.exe" goto endofperl
if %errorlevel% == 9009 echo You do not have Perl in your PATH.
if errorlevel 1 goto script_failed_so_exit_with_non_zero_val 2>nul
goto endofperl
@rem ';
#!/usr/bin/perl -w
#line 15
...[ script contents here ]...

__END__
:endofperl
[download]

They are usually converted into shell scripts, not just copied.

No, only EXE_FILES are pl2bat-ed, most .pl files are just copied, see Re^2: Why Makefile.PL uses uppercase extension?

Module::Build will try to pl2bat-ed script_files if they're in a bin directory