[AndyJackson]

And the Constitution defines such positions as Judges and Ambassadors and gives Congress the discretion to determine what other positions require such confirmation.

The Congress has determined that acting appointments to fill vacancies for a limited term do not require such confirmation. It is really very clear.

[Alberta's Child]

And the Constitution defines such positions as Judges and Ambassadors and gives Congress the discretion to determine what other positions require such confirmation.

Not exactly. It gives Congress the discretion to let the President appoint "inferior officers," but you've left out the "other public Ministers and Consuls" part of the Appointments Clause. Those are generally accepted to mean cabinet members -- corresponding to the "Ministries" used in Parliamentary system like the one England uses.