This is considered a symbolic reference, so use strict "refs" should not be in effect.

Yes, but if strictures are enabled the example still runs (and strictures were also enabled above), so I'm still confused:

c:\@Work\Perl\monks\sierpinski>perl -wMstrict -le
"system 'echo abc > 1.txt';
 open '<:raw', '1.txt' or die $!;
 print while readline '<:raw';
"
abc
[download]

Update: I wouldn't recomend it, though, as it's confusing to a reader ... Darn right!