(Incidentally, the optical drive in my last machine, a Macbook, was as good as useless. It failed multiple times because of the flex in the plastic case. So much for impeccable Apple design standards.)
Already now all the many users of floppies can pick from only a dozen or so floppy drives on Amazon. Abhorrent! And the money they have to pay for it! Way more than $10†! Truly horrific.
All kidding aside, you will be able to buy cheap external optical drives for a long, long, long time. There is no need at all to worry. The optical drive merely becomes an external add-on for those who truly need it. I also like to buy old music that hasn’t made it to “the cloud” and probably never will. I will keep an external optical drive in the closet for that purpose.
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And while I'm sure that Apple buyers were among the first demographic to ditch physical media, this development is certainly another nail in the coffin of the brick-and-mortar data archives that are record stores.
CDs will certainly disappear – and good riddance to them.
The lack of an optical drive on Apple laptops will not be the stake to the heart of the brick-and-mortar music store; lack of consumer interest will.
The social music scene is moving online. Services like Last.fm, Pandora, and user "created" content sites like SoundCloud are the future. The nostalgia of standing around a music store is nice to think about, but not particularly profitable for the owner.