Your novograd.wordpress.com will automatically lead to xyz.com as long as you are domain mapped! For example, I was vikasgupta.wordpress.com and domain mapped to vikas-gupta.in and the former leads to latter.
My PR was 4, it dropped to 0. But existing traffic was not disturbed at all. And I will get this PR back in some time. Your PR is 0 though you are getting great number of hits 3600 in a day as you say (a niche blog).
You should get your own domain as raincoaster says and you can later shift it to wordpress.org too (though it may be no so rosy; see the link timethief posted).