A note on losing 89,000 customers in 33 hours

They're just users. People reading content are just readers. Customers are people who pay for goods. For sites like Facebook and Google Search, the customers are the advertisers. The users are the product that's improved for advertisers. Or others that are scarier who get access to same user profiles/data. Why do you think they're always being more invasive of privacy and showing more ads even if people don't want that? They make more profit off their actual customers by selling them a chance to analyze and manipulate users. That simple.

Bruce Schneier was first I read on this although I can't find original writeup. Here's one:

https://www.schneier.com/blog/archives/2013/11/surveillance_...

Here's one meant to be slightly entertaining that's specific to Google's end of things:

http://www.datamation.com/columns/executive_tech/article.php...

Note: They did consolidate their privacy policies for various services to start linking things like author predicts. I found that news piece before this one.

Note 2: The "If it's free, then you're the product" meme obviously doesn't always apply to free goods. You must assume it does in U.S., though, since you have no legal protections in practice on that sort of thing. They might sell you out behind your back.

Facebook users and Medium users?

Neither of them call their users customers; only the clients (e.g. advertisers) actually paying them money.