Last modified: 2011-03-13 18:04:43 UTC
Anonymous user may add such spam - but I don't think registered user will do that, and the admins can block him forever easily. You can also disable the spam filter for admins - why should an admin insert spam?
Spambots routinely register accounts on wikis for the sole purpose of spamming. Disabling it for admins would be unhelpful, as that would effectively lock an affected page to admin-only editing.