How has music been influenced by technology in the twenty-first century when compared to the music of John Lennon?

Answer

Music is now more rock, pop, and techno.

Answer

When Lennon and the other Beatles were creating their effects back in the mid 1960's, they had really crude technology to work from. To create music played backwards effects, for example, I believe they actually fed audio tape through a tape deck backwards. They also had a limited number of tracks to work from (16-track, I think) limiting their ability to mix the music.
Now, of course, your average PC or Mac with the right software can do more than anyone at Abbey Road Studio in the '60's could have imagined.
The major impact of the technology has been to make it much easier for musicians to recreate their vision in the studio. Ultimately, however, Technology is easier to develop than a unique and interesting creative vision, so ultimately the musician of the 21st century faces most of the same problems Lennon faced: find something interesting to say in an interesting way that will encourage the public to buy your music once produced.