1. Enterprise Service Bus products include items of Enterprise Service Bus and message Broker. What's their essential difference?
This blog helps me lots: http://www.udidahan.com/2011/03/24/bus-and-broker-pubsub-differences/
The key point is Accountability.
The rule that there can only be a single publisher for a given event type is one of the things that differentiates buses from brokers, though both obviously allow you to have multiple subscribers.
2. Why we need Message Broker? Many other software can do file transforming and protocol translation and CHEAPER.
This blog gives some hint and brings me think more about the Message Broker User experience..
BTW, pls ignore the implicit Ad. for NserviceBus in the blog. I don't mean it and know nothing about this software. :P