In previous versions the URI of an entry in both Management and Delivery APIs would be the API path to the entry resource. This made sense at the time as we didn’t have a concept of nodes where an entry could be given a location on your site.
Now we have introduced nodes. It makes more sense to have the URI as null in the Delivery API if you haven’t attached it to a node. This clearly indicates that an entry hasn’t got a location on your site.
In the Management API we have removed sys.uri entirely as nodes are a delivery concern.