It should be possible to screen for emails with these embedded tracking links, based on the image server's URL in the links. Someone should compile a list of these URLs, as well as senders, and then distribute them similar to Adblock filter subscriptions. I personally don't want to see any emails of this sort, unless I've whitelisted them. This filtering functionality could be incorporated into Spamassassin et. al. And regarding personal "return-receipt" type functionality embedded like in the article, I don't want to see them either. Emails from boss? No, problem, I don't have a boss.
Regarding exposure of your IP address when opening any remote image, that really is a problem. It strongly argues for going through a proxy of some kind or functionality like gmail has (although then you get all the Goggle tracking).
Virtually EVERY e-mail client or web mail system includes an option to not view images with e-mail.
There is NOTHING unique about gmail in having an option to block images, including one-pixel “web bugs.” Everyone has that. Everyone. The only question is whether or not that “feature” it turned on to show images, or turned off to not show images, by DEFAULT.
Sometimes it is not set for best privacy and the user has to take responsibility himself or herself and turn off images.
As to the problem you cite, tracking, “although then you get all the Goggle tracking” — that is the reason to use other e-mail and not gmail.