On every platform, Perl uses the #! line to get options. But if Perl is the first one to get the -T option from the #!, then -T won't work (you'll get the "too late" error). Win32 doesn't use the #! at all. I've heard that Apache can be configured either way on Win32, but by default uses the #! line (and that agrees with my limited experience).

Okay, maybe I underspoke - perl on win32 uses the shebang line to get command line options, that is to say: a perl script on win32 w/ line 1 as:
#!/usr/bin/perl -w
doesn't care that /usr/bin/perl doesn't exist but, assuming you're doing:
perl myscript_with_shebang.pl
will use the '-w' for the script. However, -T will be 'too late' on win32.

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