So this is where the logical chain leaps from "I am on a bunch of newsletters which I don't value" to "Email newsletters are ineffective." That's a category error, right? (4:30 AM, somebody find the word for me.)
A "newsletter" is probably not the best positioning you could have for a scheduled opportunity to get in touch with a customer/prospect about something of mutual interest, but be that as it may, they're big freaking business. Billions upon billions of dollars a year. Every single time folks do one of those poll-Fortune-500-CMOs-and-ask-about-channel-ROI email obliterates every advertising channel, organic search, social media, etc etc.
Additionally: there is a different-strokes-for-different-folks effect going on. You might very well find How To Make Thanksgiving Bingo Cards boring. (God only knows I do!) I forgot to press send on that in 2010 and people found me to complain about it. In this wide world there is probably somebody who gets the Hoover email and has that be a nice little mini-highlight of her morning. She might print it out and clip parts of it. Maybe even show it to her friends.
Many of you run startups / software businesses. I'm sort of talking my book here, but if you trust me on anything, trust me on this: software businesses -- including software businesses with very techy customer bases, including techy customers who profess to hate email -- routinely figure out how to send emails that people like to receive, that successfully motivate behavior, and that repeatably generate absolute truckloads of money.
The unit economics of it are almost staggering: in quantity, emails cost substantially less than a penny to send. When you get in touch with the 10,000 people who affirmatively asked to hear from you, many of them are, predictably, right around that time in their life where they are in need of your product or service. They were busy because they have friends, children, jobs, hobbies, and a million things more important than remembering every company they have ever done business with, but if you catch them at the right moment, bam, sales process begins again. Given that getting a new customer in the door routinely costs companies hundreds or thousands of dollars, it's very, very easy to justify budgeting a whole quarter a year to keep old customers in a mutually beneficial warm relationship.