It's a timeless concept. You'll notice if you really look that Jewish people have a strong tendency to only use businesses that are owned by others in the Jewish community. This keeps the money flow in this tight knit community.
Think of your fellow dg's the same way and it might make more sense. If you need something, programming or computer equipment or anything and you can get it from a dg owned or supported business then you'd help to enrich the community by doing as much of your business as possible within the group.
Then you'd look into starting dg businesses to supply the other services that aren't covered within the community.