Email protocols were long ago standardized. As a result, people can use any of a large number of applications to read and organize their email. To my knowledge, there is no standardization amongst the various forum tools out there.
While I understand and somewhat agree with you, Skip, there is a "hidden" feature of Discourse that does make it a little easier to track many different forums: You can add ".rss" to various URLs and get an RSS feed for that topic/channel/etc.
Cheers,
Peter