Maybe you don't see it, but there could very well be an appearance of a conflict of interest here. The OP was not just "promoting Perl", he was drawing attention to your book. (Surely your hubris is not so great as to believe that your book is Perl -- or an authorized representative thereof?)
The point being, one might wonder whether you'd have been as apt to defend the post if it had been a review of someone else's book, or, conversely, if anyone else would have rushed to defend the OP against my charges — as, it indeed appears, no one else has.
Anyway, it's minor, so I'm happy to let it go.