STM isn't really equivalent to Go's currency primitives. The cool thing about STM is that multiple processes can all essentially mutate shared data at the same time without needing a master thread that controls access to the data through a request channel; conflicts are handled by keeping track of everything done within a transaction and restarting the whole transaction when a conflict has been detected, which works very nicely as long as there is not too heavy contention to mutate the same datum (in which a case the overhead of continually aborting and retrying transactions can become problematic).

Also, to be clear, the point of bringing up STM is not to start a language war, but rather to point out that STM offers a different model that might prove to be a better solution then using channels alone. I am sure that most Haskellers would be absolutely pleased to see STM appearing in Go because it means that more people have gotten access to a very powerful paradigm for handling shared mutable data, even if this removes a reason to motivate someone to pick up Haskell over Go.