When clicking the same spell over and over again, thousands of times, it is important that the sound of this skill is not repeated exactly over and over again which would dull the experience of the hack n' slash genre. Each skill is given multiple tracks for casting, pathing, and contact. Each of these distinct elements are then also given special treatment with varying sounds, lengths, and volumes. When compiled together, they randomize five to ten different sounds that can be repeatedly randomly to help add variety to the button mashing combat.
Along with this, even the music itself can be randomized. Starting with random sounds, it was mentioned that there are areas where random sounds can be heard while other times silence is used. With the actual music, it is orchestrated in multiple levels. They then use these multiple levels to help create randomized music that blends together harmoniously so that you do not even notice that the music itself has changed and is randomized.
Bridging the gap between Blizzard North and Diablo I & II was also a key focus for the team for creating the soundtrack of Diablo III. A lot of effort went in to using what Matt Ullman created for the previous games and made iconic to help bring players into the new game seamlessly. While creating something unique for Diablo III, the team made sure to use those iconic sounds. It was even mentioned how when Diablo III was announced at the WWI in Paris, that only music was needed for the entire crowd to know that it was Diablo.
If you are interested in learning more about the music and sound of Diablo III, you can watch the panel (will be uploaded soon™) and take a listen for yourself. You can also purchase the Diablo III CE which will include the soundtrack and making of.