Thats what stamps.com is, only stamps.com is less time consuming and more efficient.
Its not a problem of coordination. I have a scale. I can weigh and issue the correct postage myself (Media mail is always tracked, by the way).
The issue is the likelyhood of the package to be mishandled increases when its mailed in a manner outside the norm.
Its a handling issue as well as a processing issue due to poorly trained employees.