For the majority of websites it's not so much a Black Art as something anyone who designed websites more than 5 years ago should manage competently (assuming there aren't unreasonable requirements such as pixel perfection or reproducing every hover effect). The comparison is more finding someone that knows how to program Python instead of copy/pasting PHP scripts.
Html and css were not designed to be an arcane programming language, but a simple layout markup. If well designed then copy paste should work fine. Arguably we didnt quite make that simplicity, but I think your Python PHP comment is way off as far as html css is concerned...
