He mentions that they dropped the RSS functionality, but this is not the case at all. If you edit one of your existing alerts, you can change it to a feed.
But the blog post OP cites provides some convincing evidence that they were gone for at least a moment last July. http://googlesystem.blogspot.com/2013/07/google-alerts-drops...
I guess they changed their mind and brought them back? Weird.
$BLAH/reader/$BLAH
which suggests that, when those feeds were originally created, the delivery mechanism somehow involved GReader.
I went back to Google Alerts and re-copied each of the feed URLs and see that in the new URLs, the path looks like:
$BLAH/alerts/$BLAH
Not definitive, but it hints at some kind of connection.