Oh believe me, I'm right there with you. I would never bother trying to justify the "reality" of anything within Ravenloft, as there's no possible way to rectify everything there. None of it makes a lick of "realistic" sense, LOL.People are born in the domain though as well. And Falkovnia has one of the larger populations of the domains (the second largest settlement is located there). However I doubt they thought through the numbers here and I am sure if you crunched them realistically, you could find problems in Ravenloft (also it is generally a lower population setting than most other settings).
So I think Perkins' idea of the soulless was just one way in trying to indeed make a possible sense of a senseless situation. But as is usual, most people never even thought about it and didn't care, some people appreciated the attempt at explaining things, and some people got pissed off at how things "got changed". There's really no winning there.
I sort of see Perkins' invention of the "soulless" in Ravenloft to be along the same lines as Rob Zombie's "tragic backstory" he gave to Michael Myers in his Halloween reboot-- something that tries to give an answer to a question that few people probably cared about asking, and in some ways reduces the mystery and thus the tension of the situation for those who are observing it.