At this point, there's a big debate on the current validity of the album format that came into prominence into the 1960s. The truth is, even the album format has changed significantly for the majority of music consumers. When CDs came into the picture, album lengths became stretched out (often for the worse), and the "two side" format became more rare. Great artists will always make albums, but for the average consumer, music culture is now definitely single-based.
Like everything Apple does, they stole someone else's invention and made it into something "revolutionary," making people think they invented the digital download system. They didn't. However, they did blow it out of proportion. Sure, they still have the DRM spyware encrypted on their music files, but they expanded what Napster and others started. They made digital downloads more accessible. Why bother going to the store when you can pay $10 right at your computer to get it instantly? Why not just buy a single song? Back in the days of LPs and cassette tapes, you couldn't buy a single song - stores only offered full albums, and the individual songs were sold to radio stations as singles for airplay. Now, you can buy one song or a whole album. It's reducing the cost of making albums, as there's no need to print out all the CD labels and artwork and buy the discs and cases. The digital download revolution changed it. ITunes is the one responsible for making it really happen, even if Apple stole the idea like they always do.
iTunes has definitely changed the way people buy music, more than anything else in the history of the music business. Though it wasn't the first digital distribution outlet, or even the best in some people's opinion, the market saturation of iPods and iPhones has almost made iTunes into a generalized term for purchasing music (like Coke for soft drinks, Kleenex for tissues). With all that said, the subscription model (Spotify, Pandora Radio, etc) threatens to change the relationship between the consumer, the music music business, and the music itself even further. Whether iTunes will evolve to be a part of that evolutionary change remains to be seen.
Apple's iTunes had definitely had influence on the way people consume music. These days much more people buy music digitally and listen to music through things other than CD's. Apple is one of the leader in this new trend and have changed the way people consume music forever. I think most people will not make the switch back to CD's either.
Apple and their iTunes program may not have invented the system we have now with their music program, but it revolutionized the digital music distribution industry and paved the way for many to follow, be they downloadable programs or on-line applications. It has grown to now manage podcasts, tv shows, movies and audio books, among many other media.