Like my wife said one time: "If you were cheating on me, I wouldn't know how to track it online." Not because she's not technologically adept, but because she's seen me using proxy servers and disposable emails that she knows I wouldn't be dumb enough to do it in plain sight. Just like it'd be moronic to receive love letter correspondence at my home address, it's moronic to receive it at my main email address.
I'll also clarify further. The woman prosecuting is a moron for using her normal email address (with her password in a book next to the computer) to conduct an affair. If you don't try to hide it, you're trying to get caught. I'm sorry, I was computer savvy enough at 4 to start up a PC and use DOS to load a game. A 6-10 year old today would beyond the shadow of a doubt be able to access her email - therefore it was unprotected.