this is really interesting and a classic dilemma caused by web anonymity.
pierre's young. maybe he does go through these forums just for kicks. who knows.
however, i personally don't believe it was pierre. their aversion to people who stick their noses into their personal lives have been pretty much apparent over the years. i remember from an article years ago where caroline said that her kids, since they were very little, have always seen the photographers as their enemy or the bad guys. and over the years media attention hasn't actually mellowed, and i'm assuming their sentiments toward the press haven't either though experience has taught them how to deal with the fanfare.
i'm pretty sure they feel much the same way about people who patronize the photographers' work, and that would be us. imo, pierre or any other well-known royal for that matter, wouldn't go around reading forums about them where people speculate, criticize, and even ridicule aspects of their personal lives.