There are at least 2 things with web designers sites. (there are more but this is just an example)
Did they design it from scratch or are they using some kind of grid/gfx-template system?
Did they actually code it and not use an existing CMS?
I code all my sites from scratch, I don't look to any CMS, although have no problems with coding with any of them.
As a software engineer I code with reuse in mind and build in essentials which will benefit the sites I work on.
Going forward though looks I'll have to look to support other CMS as more and more people take those up rather than want purpose made sites/blogs/pages.
The net is becoming saturated with designers all chasing the elusive client, there are probably other professions that are equally seeing this influx but online developers and designers are just exploding.
As Andy said, look to some of the other sites and see how they are doing things, I also recommend looking at other issues such as usability, accessibility with WAI etc.. atm they don't seem important to some as some of the issues cannot be seen or not even thought of from the designers pov, however, going forward these will play a bigger part and it will become essential to incorporate them into your work.