The two saved searches look similar but have a different scope.
The Newly Discovered Software list is only inventoried components that are not associated to a software product.
The list in the Software Catalog, you'll notice, is labeled differently - "Newly discovered software/undefined software." It is the newly discovered list plus all other non-inventoried software that is not currently associated to a software product. It is typically deliverable software (software releases, service packs, software updates).