I've read on here a few times that even big name celebrities don't have bodyguards. Lots if not most celebrities have bodyguards, for instance Justin Timberlake, Beyonce, Ashlee Simpson, Celine Dion, R. Kelly, and the Backstreet Boys, Diddy, Britney Spears, Angelina Jolie, Nicole Richie, Olsen twins, Oprah Winfrey, Tom Cruise, Snoop Dog, Lance Armstrong. It only took me a couple of minutes to just find these names. I'm sure there are lots more.
Kate and Jon are no where in their class, but we have no idea if they have gotten death threats, or need the bodyguards just to walk into places, or to be shielded from over enthusiastic paps. They may have stalkers, or even fans who want to get a bit too close. I remember a story where a fan stalked David Letterman, and his bodyguard caught her breaking into his house. I don't think it's unusual at all, when you illicite so many feellings from people. Just read the hate boards (or even just regular boards)...some people dislike them so intensely that it would make me nervous to be close to them, so I could see where I would feel better having a body guard.