Thinking that a web designer's job is to convert PSD to HTML is a pretty washed down concept of the profession. Albeit, converting PSDs to HTML is merely a particle in the universe of the things a web designer is and should be capable of doing.
Learning web design is an ongoing, never ending profession, like any other profession. Web design has all the things you mention and universes more of things in addition to that.
SOME basic responsibilities of a web designer are:
- Provide guidance in areas of UX, UI, design, accessibility, performance, branding, scalability, SEO, maintenance, collaboration.
- Learn the intricacies and customs of the target group the project is intended to serve.
- Understand the technicalities of the web at all levels.
- Have an open mind to learning about other areas and professions that are tangential to web design.
- Become a thinker of solutions rather than staying as a doer of requirements.
- Share, share, share their knowledge.
I've been doing web design for more than 10 years and I'm still learning ;)