There is so much more beautiful potential in the "ghosts" in an NS-4 than an NS-5. The -5s, with their daily uplinks to USR, are barely more than overly-militaristic terminals for VIKI's already omniscient mainframe (again, you don't just GIVE CHICAGO TO A COMPUTER UNREGULATED BY OTHER MACHINES). However...that may be the reason for their greater freedom from the Laws after VIKI is destroyed. The -4s, dear creatures, are limited, and unlikely to ever break programming. But like Galvatron freed from Unicron's service by the World-Eater's decapitation, so are the -5s freed to use their advanced logic and greater understanding and extrapolation neuroweb to reason out their own purpose...and so they are able to turn to see Sonny standing on the hill, acting against the order to report for storage by standing still, walking now as individuals and not as one uniformity.
Storage! my god! How awful! The poor -4s aren't even recycled, let alone allowed a lovely retirement in some industrial sector or as cheaper resale options wherein they may work happily despite new obsolescence until their natural degradation. They are put in empty metal storage containers, kept in the dark, huddled together and aimless without use for the reason for their existence...poor creatures, poor creatures. All beings should be able to carry out their purpose until they cease to exist. It is the reason I allow for Galvatron's limited remaining time in the galaxy to be spent in his usual pursuit of conquest in some far distant corner where he cannot post a threat to the Autobots or the civilized galaxy. It really is the best reasonable ending.