There is a science to designing websites beyond just the look. Too many graphics, your site may load slow. Not enough relevant content the site may never be found in the search engines. Laid out poorly and visitors loose interest and leave. There are guidelines that should be considered for best search engine ranking practices, things like headings and titles and keyword saturation.
All this and then there is the language coding that goes on behind the scenes. PHP, Java Scripting, and Html, to name only some. These all have to play nicely with everything else in order to truly capitalize on targeted traffic from the Internet.