Even in this day and age, my former employer Inventive Designers refuses to send out an email to all customers when a new version of their (closed source) Scriptura product is available. They only send a notification email to those customers whose bugs have been fixed in the latest release.
One of the scripts in my bag of tools to check whether a site is still up and running is content-check.pl. This little script compares the hash of a web page against a previously created reference hash. If the content of the web page has modified, this script will detect it and send an email.
You have to be very careful which page you check because even the slightest difference in the HTML source will be detected.