Business Newsletters not big spam source

Arial Software performed an audit of the email subscription practices of over 1000 companies.
What they found in their study is that signing up for a newsletter from a reputable business doesn’t get you onto any spammer lists. However, even big name companies have problems in unsubscribe requests and don’t follow what Arial feels is a best practice of double opt-in. (They dont describe double opt-in that I saw, but I assume that is where you subscribe via webform and are sent a url via email that you must click on. Then they send you another confirmation that you are really in.)