It's a bit of a catch-22: you can't know that there's not much different between x86 and x86-64 until you understand both. I guess asm newbies have some kind of mistaken idea that x86 is irrelevant and not worth their time learning (even if it were completely dead in the wild, which it absolutely isn't, you still need to know it truly understand the architecture); I've tried to post older x86 and ARM assembly language guides, much better written and more in-depth than this article (no offense intended to the author), and the only comments I get are along the lines of "this is old, it doesn't even cover x86-64/ARM64."
