Why does Armory enforce a minimum transaction fee? When I send coins using the standard bitcoin.org client I can set the transaction fee to 0.  However in Armory client there is a transaction fee of .0005 and you cannot override it to less.

I was under the impression that transaction fees were set by the user, and that the transaction fee determined the priority of your transaction on the network...so why does Armory force this?

In fact when I sent coins with fee of 0 via bitcoin client it went through faster than when sending the coins back with a fee of 0.0005 with armory...?
If the coins it is using have a lot of confirmations, the less likely a fee is going to be needed.

In the instance reported here, when the payment was sent using the Bitcoin.org client the funds had many confirmations and no fee was required. 

When a payment for that same amount was then created using Armory, the funds did not have many confirmations and thus the client insisted on there being a fee.

This is not a difference between Armory and the Bitcoin-Qt client.  This is a difference between sending coins which had lots of confirmations versus sending coins which had fewer confirmations.   The same thing would have happened regardless of which of the two clients was being used.