> His ignorance was as remarkable as his knowledge. Of contemporary literature, philosophy and politics he appeared to know next to nothing. Upon my quoting Thomas Carlyle, he inquired in the naivest way who he might be and what he had done. My surprise reached a climax, however, when I found incidentally that he was ignorant of the Copernican Theory and of the composition of the Solar System. That any civilized human being in this nineteenth century should not be aware that the earth travelled round the sun appeared to be to me such an extraordinary fact that I could hardly realize it.
I suspect that Doyle gave Holmes this dialog because it was reflective of the character, not because Doyle thought it was a good description of the way the world or the mind works. If you read enough Holmes you can see pretty clearly that his character is very rarely the voice of the author—that's Watson, who admires Holmes's skill but is frequently frustrated by him as a person.
I'm not even really convinced that Holmes could be as skilled as he's supposed to be with as broad ignorance as he's portrayed here as having. The science of deduction as he's supposed to apply it in the stories would actually require rather encyclopedic knowledge of many different topics in order to understand the wide array of humans he's supposed to be reading (and indeed, in later Holmes stories he exhibits this kind of encyclopedic knowledge of extremely obscure details of many fields).