Automatic Update of Beta Apps

A few reasons:
1) There are hundreds (thousands?) of apps in beta, and the database for the updater is manually updated by John himself. Adding all the beta apps would take so much of his time that he would never have time to update the platform or make the money he needs for hosting costs.
2) Allowing anybody to modify the database would expose all of us to viruses and malware, as anybody could post a virus-filled app that has the same AppId as another good beta app.
3) A lot of beta apps do not get updated regularly, and some never get updated at all. John doesn't want or need the hassle of people complaining when a beta app isn't at the latest version.
4) Beta apps are hosted across too many different hosting sites, dropbox folders, developer websites etc. to keep track of. A lot of them will not support the silent download system that the updater uses.

I'm sure there are other reasons too, but those are enough for it to never happen, I think.

When you get a beta app and test it, comment on the topic with a "It works well." or something. Then, you'll get updates in My Recent Posts when the dev updates it. Or, if you prefer email updates just subscribe to it. Although I think the former is a better choice.