Not quite, it's not a separator, you can't add arbitrary content after the dot. Dots are just ignored in Gmail, so you need to keep a map of dot placement and quantity to service, vastly less convenient.
Yes, you're right. The dots thing isn't as powerful as the + separator. But it is useful for sites that have a poor understanding (or regex) associated to their address validator. In context of the parent comment, that's the point, that the dots aren't restricted as the plus separator can be.