Two weeks is ridiculous. You might as well not send a newsletter. Depending on your service, pretty much everyone on your list will, at one point or another, go two weeks without a trackable interaction.

I've personally seen (opt-in) newsletter subscribers go many months without loading images or clicking a link... but send them a notice that their subscription is being turned off as a courtesy and sure enough a sizable percentage click the "keep me subscribed" button.

How would you know if I've opened your e-mail? Active html in emails (which would allow image-bugs to work) is disabled for most people that I know.