Well there's your problem. Old houses have lead. It should be assumed to be that way unless there's reason to believe otherwise.
It'll be another 50+yr before most lead paint is gone. The fact of the matter is that labor is expensive in this country so lead paint is rarely dealt with unless it's conveniently within the scope of other work.
I don't think this article very meaningful unless we have more data points. Is base housing more or less likely to contain lead than similiar quality housing in other cities?