'viral' is a term usually used by opensource detrators because of it's negative connotations.
If O'Reilly has given it's own copyrighted material to perl, under the same terms as perl, then that means they have given away certain rights to that material, it doesn't mean that they have gained any rights to perl at all.
Perl is distributed under both the GPL and the perl Artistic license. Anybody using perl can choose which license they wish to use, so it doesn't even need to be to GPL. And if they don't actually distribute perl, they don't even need to state which license they are using perl under.
The only 'control' of perl that O'Reilly has is that if the perl license changes in future, the file contributed by O'Reilly would have to be removed if they didn't agree to the new license. That's it.