Why is the Mastercoin Exodus address used in every mastercoin transaction? Mastercoin initially did fundraising through 1EXoDusjGwvnjZUyKkxZ4UHEf77z6A5S4P. It now seems to be used in every Mastercoin transaction (it has been used in thousands of transactions). 

Why is the address still being used in every mastercoin transaction? Is this built into the protocol somehow? I suppose it could be a spam prevention mechanism, but I would think the bitcoin transaction fee already prevents spam.
This was a shortcut to easily identify all Mastercoin (now Omni) transactions. We considered removing it when we were concerned our transactions might be identified that way for censorship, but that never happened thankfully. If you list all transactions to 1EXoDus, you list all transactions in the Omni protocol.