Question is whether it's losing oil or burning oil.
My theory is this (I have no evidence to support this theory, but it seems logical):
If it's only losing oil, at a half quart a week, it's getting the equivalent of regular changes. But you should still change it once in a while just to be safe.
But if it's burning oil, most of the solids will be staying behind. So in spite of all the oil being added it should still have regular changes. Or at least regular filter changes to get rid of the bigger solids, and then a full change once in a while to get rid of the small stuff that doesn't get filtered out.
If it isn't dripping oil you have to assume it's burning oil. And to explain a loss of half a quart a week, it would have to be dripping a lot.