Just for discussions' sake,

What is the difference between buying pre-owned original 360 games, and pirated 360 games?

Example, person A buys brand new --> he puts money into the hands of the game companies / etc.
Person B buys second hand from person A
Person C buys second hand from person B
Person D buys second hand from person C

The way I see it, Persons B - D effectively do nothing to support the industry, and so how different is this from piracy?