Remember when (at least in the books) Gandalf states that a "power" exists in the Shire as well? Methinks that Hobbits create a zone of chaos wherever they go. Look what happened when one or more of the four were present:
- Five Nazgul fail at Weathertop.
- A Ranger is caught off his guard.
- Nine Nazgul drown.
- Fight ensues at the "Last Homely House."
- Snowy mountaintop explodes.
- Cave troll falls.
- Dwarven bridgework collapses.
- Balrog fails.
- Gandalf falls.
- Dwarf caught off his guard.
- Steward's son dies.
- Uruks fail.
- Gollum is captured (think about it).
- Other Steward's son loses mind.
- Winged Nazgul fails with Ring in plain sight.
- Orthanc falls.
- Saruman dies.
- Shelob fails.
- Fight ensues in Tower of Cirith Ungol.
- Gollum falls.
- Rohirrim become blinded to female warrior in their midst in plain sight.
- Mumakil fail.
- Witch-King bests Gandalf.
- Steward takes flying leap.
- Minas Tirith almost overrun.
- Aragorn gets trampled by Battle Troll.
- Sauron falls.
- Pippin catches bouquet.
And so on. The reason that book Aragorn quarantines the Shire is not for the benefit for the Little Folk, but to protect the rest of us from them.