Does SOA Require an ESB?

Forrester's Ken Vollmer takes issue with my inference that a BPMS truly layered on SOA must include an ESB in order to achieve the "loose coupling" promise. He writes:

I guess the one point I would argue with you is that you seem to equate SOA with ESB?s and that is not a good way to think about it. SOA existed way before ESB?s in the form of CORBA and DCOM technology. So ESB?s are a newcomer to the SOA world.

Also, ESB?s are just one alternative for achieving SOA. The other major options are application servers and BPM Suite products. Both of these have ESB features and much more baked into their solutions.

Just so you know that I know what I?m talking about, I cover ESB?s, BPM and SOA at Forrester. CORBA? DCOM? Loose coupling? I guess I don't know what I'm talking about! Whatever, Jesper's post I referenced yesterday still computes better for me. By Ken's definition, BEA already has all 3 ways to do SOA - an app server, BPMS, and ESB - without even putting them together!

But I don't think I'm the only one confused on this issue. There is a long thread on Yahoo Groups in which some heavy hitters weigh in on the relationship of SOA to ESB, and come to no recognizable conclusion.