[Rumil]

I had the impression that Elrond was referring not only to the Dunedain guardians but to the abilities and character of the Hobbits themselves. Although primarily peaceful, when danger threatened the Hobbits could band together for self defence, as they appear to have done during the Fell Winter and the Battle of Greenfields and as, after a little prodding, they did at the Battle of Bywater.

I guess this also brings in the stable settled nature of the Shire and the deep co-operative links that bound its inhabitants together (in a sort of 'still waters run deep' sort of fashion). One might say that Hobbits are, essentially, good folk and would look out for one another at times of crisis.

To speculate wildly, maybe their peaceful way of life had also attracted some indistinct and nebulous protection from the great powers, the Valar or even perhaps Eru. Did Gandalf perhaps subconciously display the wishes of his masters by his benevolent regard for the Shire Folk?