"As a rule"

[Elianna]

Often when Tolkien is writing about the Hobbits he'll throw in that they perform some part of their culture "as a rule."

Their faces were as a rule good-natured rather than beautiful.

Not very expensive ones, as a rule, and not so lavishly as on this occasion; but it was not a bad system.

as a rule dwarves said little and hobbits asked no more.

Only a few words of it are now, as a rule, remembered.

My interest has finally been piqued. Why use this phrase? For it to be so prevalent, surely Tolkien had some idea behind it. What's it say about Hobbits that they do so many things "as a rule?"