Strictly speaking, CD's is correct because CD is not a word, as apple is, but an initialism. The rule of putting an apostrophe before the "s" in certain plural constructions was well established in the 20th century, but has fallen into disuse and overuse. It is not uncommon to see "'s" used (by those who should have re-done fifth grade) to pluralize normal nouns in handwritten shop signs, for example. So the language (and its typography) is evolving away from the rule because the lower 48% found it hard to keep straight.

I think there are good AND bad reasons for defending shifts in language. The good reasons are when the shift is slovenly or ignorant and causes a loss of clarity in current exchange. The bad reason is because "it ain't how I larned it", a curmudgeonly resistance to change. Change will not cease because of tantrums or resentment, which most 11-year-olds realize are a total waste of time.