I think there is an additional reason for using disembedded libraries:
When you use embedded libraries and you have lets say 5 addons which use library xyz, and library xyz gets updated, next time you update WAU will download all 5 addons because of the updated embedded lib.
With disembedded only the changed library gets updated.
On addition to update more packages with using embedded, the downloaded packages are also much larger.
So using disembedded libs is way less load on the Wowace servers.