If someone you hadn't heard from in years e-mailed you out of nowhere, wouldn't you write back? Wouldn't you write back out of curiosity if nothing else? People's lack of curiosity (as well as their lack of so-called "common" courtesy) depresses me.
Once or twice a year I e-mail my college boyfriend. We met ten years ago, broke up eight years ago, and haven't seen each other in six years. But has he ever responded to any of the twelve-or-so e-mails I've sent over the last six years? Nope. Why? The answer is simple: He lacks courtesy and curiosity, and could give a shit about anyone but himself (not that this has changed since I knew him). In short: He's a douchebag. Our breakup was as amicable as one can be when the participants of the doomed relationship are twenty years old. If someone I'd not heard from in years e-mailed me -- especially if that someone was a person I purported to be in love with at one time -- I would totally write back. My morbid fascination with the unknown wouldn't allow me not to respond.