That's right. BPEL was designed to work with web services only. That's why you can use it natively there. in jBPM5 because we support any type of interaction you need to create a new WorkItemHandler (or reuse one) for each type of interaction. You can try creating one abstract enough to be used in different scenarios via some parametrization or configuration.
I'm not sure to understand completly your last paragraph (it was a question?). But in a brief yes, you create a WorkItemHandler that it's associated using a String to a specific runtime. That means that you can have different runtimes that uses different handlers, this is usually very interesting to deal with a process execution in different environment, like for example: developement, testing & production without changing anything inside the process.
Greetings.