I never said that DRM and the agency model were related. I was merely pointing out that Apple's entry into the ebook market removed seller freedom and empowered publishers. This was in contrast to the parent post which stated that Steve Jobs brought freedom to music by removing DRM from music formats.
I personally think that Apple was afraid of losing too much of the ebook market to Amazon so they made a behind-the-scenes push for publishers to adopt the agency model to thwart Amazon's price advantage. This enabled them to enter the ebook market using their shiny iDevices and sell content at the same price as Amazon. Apple's policy change to require a 30% cut of in-app purchases further pushed their advantage and forced the Kindle app (as well as other ebook apps) to remove their "Store" button that launched Mobile Safari to the Kindle web store.
As to whether the agency model is better for consumers is arguable. It is good that there are more choices in the market. Having an Amazon monopoly on ebooks would be bad, but Apple's tactics to bully their way into the ebook market are pretty ruthless. Such ruthlessness can only be attributable to Steve Jobs' desire to have Apple control all consumer content on iDevices. iBooks is still somewhat of an afterthought compared to iTunes' offerings in terms of music and video. For example, why can't I read iBooks on my MacBook Air? Why can't I access my iBooks by a web browser (ala Kindle Cloud Reader).
I'm not an Apple hater. I own a MacBook Air and an iPhone. I think iDevices are very nice, but I don't think that the agency model is good for the consumer. It drives prices up and reduces the ability for ebook vendors to compete in the market.