When the V3 installer was built we wanted to be paranoid enough to be able to wind back installs so a variety of stuff is saved prior to an update.
Amongst this was the webapp folder and the dist folder.
In 3.4 the webapp folder is now under the dist folder and the result is that in fact a large chunk of what we are saving is the precise distribution.
Given that we have had no install hiccoughs during the V3 lifetime it seems needless to save the dist folder away moving forward. This does not affect the ability to rollback, rather it makes it harder to rollback (you need to do a clean install of the version and then copy the files over it).
I propose that we do this early on in the lifetime of V4. We may not want to do it it in V4.0 since that will be the first distribution of a reasonably complicated update (for instance we may be changing property names and we may be moving files about.