Narayan,
I think that the persistence.xml files were included in the jbpm-bam module because it wasy the ... quickest and easiest (and most obvious) solution.
That's not to say that it was the best solution!!
I've been looking at this as well and wondering about what a better way would be to set this up: if you could, I would be really interested in hearing what would have been a better solution!
Thanks very much,
Marco