What does this mean to the typical small distributor?
If you have 1000 customer contacts and your open rate is 35%, you get 350 real opportunities to say something to your customer base. With normal sales calls hovering in the $250-450 price range, that equates to some real bucks.
This also allows you to reach those secondary contacts too. These are the people who sometimes use your products. It might be that test engineer who needs your products once or twice a year. Your sales person can't justify calling on them, but with a email newsletter you stay in contact.