The beginning of the article describes how the author would pay much more than $6 for $6 worth of electricity. This is called consumer surplus, and is the principle that people usually pay less for something than the maximum price they are willing to pay, because they are paying the market price (to oversimplify slightly).

This principle is relevant to Hacker News, because I've often seen statements that the value of something is exactly what people are paying for it. Taking consumer surplus into account, what people pay is an upper bound since they may be getting much more value than they are paying. People won't pay more for something than it's worth to them, but they may be paying less. (As a startup-related aside, one reason to have different pricing tiers is to collect as much of the consumer surplus as possible, by charging more to people who will pay more. Coupons and discounts are another way.)

http://en.wikipedia.org/wiki/Economic_surplus