I disagree that the optical drive is used 'very unoften' by a minority. Do you or anyone have proof or research study that says the "majority" of Mac/PC users no longer use their optical CD/DVD drives?
People must remember that the so-called "Cloud" is still in its infancy. A little over a year ago, even Apple was reluctant to use the word "cloud", right before it decided to jump into the "cloudy bandwagon", then releasing iCloud only in Summer 2011.
Hence, my point is the "Cloud" is still a fledgeling technology, not a proven medium of storage in terms of accessability, reliability, redundancy, or ubiquity in the same way that CDs and DVD-R/DVD-RAM have proven themselves for many years. At the very least, Apple should have waited another 1 or 2 years before it phased out the built-in optical drive from its iMacs.
NOW.... before someone retorts that we can always buy an external optical drive (Apple sells a nice USB one, I understand)..... PFFFT, because you just failed to comprehend the meaning of an "all-in-one" machine.