despite 90,000+ signatures on an online petition (though a quick skim of a few signatures suggests that not all of them endorse the petition's views).

Good for Wikipedia. An encyclopedia may certainly choose not to include such pictures, and still remain true to its mission. (I don't think it would be right for the encyclopedia to remove important historical details that some people are offended by, though the encyclopedia authors would surely have the First Amendment right to do this; but drawings representing the subject are not a necessary part of an accurate discussion of the issue.) But I think an encyclopedia may also properly refuse to succumb to such pressure, and I approve of the Wikipedia editors' refusal here.