The increasing demand for HD content for media consumption and rich formats such as HD DVD and Blu-Ray drives the demand for high capacity disk drives solutions in the end-user market.
In the book, Christensen describes how innovations on the low-end of established markets, from discount retail to disk drives, have made dramatic gains in marketshare.
So if an organization decided to buy even more disk space to try and increase their performance, they actually end up over-purchasing and under-utilizing all of their storage capacity for miniscule gains.