I don't follow the reasoning; wouldn't it be more sensible to compare ZeroMQ vs. TCP instead of ZeroMQ vs. HTTP? If you can so easily replace HTTP, why the fuck did you choose it in the first place instead of a plain TCP protocol?
ZeroMQ is not really at TCP level, ZeroMQ is about sending messages to and from various semantic endpoints, such as REP and REQ sockets, specifically made for doing RPC. If I was using TCP, I'd have to do a _lot_ of work myself (keeping the connection up, throttling locally when it's not up, keeping track of which messages goes where, etc).
