Federated ESB - No single ESB per organization

That's a hot topic here.
I've heard this couple of times in the past, though got the "official" legitimation to use this.
Most of our customers tend to see the ESB as a single centralized ESB for all purposes in the organization.
Seems like mid and large size organization will not be able to work with a single bus, but will rather use several buses in different patterns.
This will be referred as Federated ESB pattern, and we expect each domain zone to have its own ESB.
For an example, one could think of large retail with department stores. Each department has its own domain ESB while the centralized datacenter has its own ESB.
For these cases, IBM has several solutions for ESB - WMB, WESB, WDP - these all provide different answers for different requirements.
There are technical differences between these ESB implementations and therefore they can be relevant for different purposes.
Seems that IBM do not see to much overlapping - mainly from the prospect point of view. I have heard couple of times, from differect executives, that the 3 products are here to stay and keep on being developed with full engines.