Any analogy based on a technology that is no longer commonly available is null and void. Can you walk into any store and buy CDs and DVDs with audio and/or software? Yes. Cassettes? Not so much.
As previously mentioned, the invention of the keyboard far predates today's, and yesteday's, physical media. And yet, people still seem to want a keyboard with their computers. Hmm. And, umm, electric start with their cars, although that's a really old invention too.
The question is not how long ago the technology was invented, but whether its intended replacement is a viable alternative. In the case of optical media, for many people that post here digital distribution is viable. But for a significant number, it is not; and it would be fair to say that the universe of people that post here are further advanced than the typical technology consumer.
For people looking for lightweight and portable, sacrificing the convenience of an internal optical drive although they still use optical discs on occasion is understandable. For people looking for an all-in-one computer, it isn't. And no, many people on this board will never, or rarely, use it. But that doesn't mean that the majority of iMac purchasers won't.
This week I used my drive to rip the soundtrack CD that came bundled with my Diablo 3 collector's ed. If I needed to first buy an external in advance, and then remember what drawer I stashed it in (or let it add clutter to a desk, quite the opposite of the goal of an all-in-one), I would have found that very irritating.