12 months is barely enough to scratch the surface. I look at my code from 10 years ago, and it's absolute crap.

Modern web development is not just knowing one language, it's a bunch of technologies, and many of them seem deceptively simple, while they aren't. Just off the top of my head of what I use as a web developer:

1) HTML (and DOM) and XML

2) CSS

3) Javascript (+jQuery +JSON)

    1,2,3 include

    a) the knowledge of different versions 

    b) browser compatibility issues

    c) how to write it properly and efficiently

4) Different image formats, proper compression. CDNs.

5) Unix shell + apache configuration + deployment

6) Database + SQL

7) Memcached (or alternatives)

8) Various tools like firebug, profilers, http sniffers, etc