DLC with added content would have an effect (like FoV/DKS). If it is just extra features, though, I'm not sure how many of the original reviews would be updated. Of course the DLC itself would get some reviews, but probably not as high profile.
Whether extra features are added as DLC or in a patch, that would also mean another set of QA and additional testing procedures (for the update itself and compatibility with previous saves) compared to getting them in before the original release. It is easier to justify that for large updates (extra content, etc) or very small ones that wouldn't need much testing. Before release there is more flexibility in adding features.
