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Just paranoia, may be. but there's enough articles out there, ie.:

How to Sterilize a Shaving Brush
By Constance Barker, eHow Contributor
Shaving brushes offer the age-old technique of applying...

I use Borax mainly because it's an insecticide and a disinfectant. Guess that they feel that their cleaning process is adequate.
What I find interesting is their comment 'not' to face lather!