Our air compressor broke. It's a shame, because I think it was old enough to donate to the Smithsonian.
Without Amazon: I could decide to go to Sears, or Wal Mart, or Lowe's, and get a new one. Then I'd have to shop around, find the one that looked best, and buy it.
With Amazon: I pull up the air compressors, price compare, feature compare, and MOST importantly - look at the ratings. I can find one that has hundreds of positive ratings, plus the features I'm looking for, plus a decent price. Two clicks later and it's on the way - it will be here in 2 days
The ratings feature is huge. It lowers my risk on the purchase. From the manufacturer's point of view it creates a small barrier to entry. There were pumps that looked nice - but they had no ratings. I didn't want to be the first - not on something as basic as an air pump.