I'm absolutely no mailing specialist, but here is my take :
Your study is quite interesting, but has it any value without you saying which mails your read when ?
Tracking if an email has been read or not is quite simple, providing the email is sent as HTML and the one who reads it is no privacy-nerd (noscript, ghostery, other ways to block external ressources, highly secure mailbox softwares, etc). What if you regularly "read" Obama's mails and not Romney's ones ?
If I were to manage this kind of mailing campain, I'd probably put on hold for a while email addresses who haven't read the last X mails. On the contrary, I would go on sending mails to people reading them. Etc.
Please tell us what you did "read" and when, and what you did not.