There are plenty of scenarios where orchestration is an unnecessary addition to service bus processing. Recall that an orchestration's prime benefit is the injection of a stateful, sequential series of steps to message processing. If the "processing" of a message can consist solely of the core BizTalk messaging components (receive ports, send ports, pipelines, maps, and subscriptions), then a messaging-only solution is the way to go. A general rule among BizTalk architects is that you avoid orchestration and concentrate on pure messaging when at all possible. This isn't because orchestration is intrinsically bad but rather because many situations actually don't require the overhead and complexity of a workflow.
That said, how nicely does the BizTalk bus play with WCF services when no orchestration is involved? Quite well, thank you. Let's look at how we may route inbound data to a WCF subscriber using only the message bus.