I agree, @moreadviceplease , that a deferral definitely means you should move on, get other apps out there, and realize that you probably will not get into that school. In fact, odds are probably against being accepted in the RD round.
But in some cases, the news in the RD round is positive. Because that chain of events (deferral to acceptance) is less common, it has sort of been accepted here that a deferral will lead to a rejection or an unresolved WL spot. And that, while likely, is not a guarantee.
Which is why the schools don’t simply reject everyone they don’t accept! (Although yes, they really do string along way too many!)