Rich Turner takes a pop at WebSphere Message Broker here.
I think he's being a little playful in his implication that you can't build an ESB with broker because of its support for WebSphere MQ - but he does cover some important points.
Firstly, of course he's right that an ESB has to support open standards - how else are any new open-standards-based applications expected to take advantage of the services on offer via the bus? And in many cases, focussing primarily on open standards, web services, etc., is just what you want when implementing your ESB. Our forthcoming WebSphere ESB product provides just this functionality.
However, there are also large numbers of cases where you need support that goes beyond this. We offer WebSphere Message Broker as our recommended tool for delivering an ESB that integrates both standards and non-standards based applications. We can argue about where MQ sits in the standards spectrum but broker's deep support for MQ is obviously a huge plus.
As for whether adding SOAP support was a "stretch" for Broker's Hursley developers... I'm sure they'll take the suggestion good-naturedly as testament to their technical prowess and of the superior architecture of the product :-p
Incidentally, my first job in IBM was testing Message Broker (before it was called that...). I'm still officially based in Hursley but now live in London. I wonder if that means I count as a Hursley Blogger. James?
[EDIT 071205 1502 to fix link]