Short answers, pulled from the story.
The Atari 2600's GameLine service allowed users to download full games in 1994. This early experiment used telephone lines but did not provide downloadable content for existing titles.
Acquiring all downloadable content for Rock Band cost $5,880.10 by the 12th of July 2012. The game featured the largest number of downloadable items among console games and added new songs weekly between 2007 and 2013.
The Dreamcast became the first home console with standard online support in 1998. Downloadable content existed on this system despite limitations from narrowband connections and the 200 block memory limit of the Visual Memory Unit card.
As of 2010 downloadable content accounted for approximately 20% of video game sales revenue. Developers began using profits from existing series to fund new intellectual properties or sequels.
iPhone OS 3 enabled downloadable content through applications bought from the App Store beginning in 2009. Apple allowed developers to offer such content in free apps by October 2009.