Well, I've always considered ATM to mean air traffic services, airspace management and air traffic flow management. As an ATCO I thus consider my duties to include in addition to just air traffic control service also
flight information service, alerting service and air traffic advisory service. So I guess ATM officer might even be a more suitable title than just ATCO.
Of course what I'm paid big bucks (
) for providing is actual air traffic control service, keeping aircraft from hitting each other and so on, and the people who only provide let's say flight information get paid quite a lot less. Why ATCOs get more money may in some cases only be a result of effective labour union policy, but ATC is what flyboys usually want to receive, not just FIS so I guess it's only fair.
I don't really mind if a flight information service officer's decision is equal to mine, after all it only applies in his field of service. I mean, as long as people are competent, (and ATCOs get the money they deserve 
) what is the real problem even if you are all included under the same title?