That only happens if you enter your passcode then see the "Trust this Computer" prompt on a computer that has iTunes installed and you click "Trust" at the prompt. That creates a set of sync keys that the iOS device will then accept to access the various services.
The article made that very clear. But it's not clear to me where these keys are stored - is it on the disk, unprotected, or is it in your encrypted keychain? If the former, it seems to me that - unless you encrypt your computer's hard disk - this means anyone with unfettered access to your computer could get at these keys and thereby get at everything on your iOS device. If the latter, it would be much more difficult to do, even if they otherwise got access to your account.
The guy said he uses this to monitor his kids (which, depending on their age, might be a bit jerky in my opinion). However since he seems like an overzealous parent, I'm wondering if he has his kids' passwords etc., which would be necessary if these keys are in the keychain.