Most folks are in agreement that Apple revolutionized the digital music industry, and the music industry as a whole, when it launched its iTunes store in April of 2003. At the time, there was no other service offering easy access to digital tracks for $0.99.
And I would argue that it did the same thing for digital movies and TV shows when it added them to iTunes in 2005 and 2006. No one came close to what Apple was doing in the space back then. And judging by the latest numbers, that still holds true today...