SEO, by its very nature, requires changes to the construct of the web pages in the site being optimizated. Because of this it’s usually easier to integrate SEO with web design on the initial construction of the site.
By doing this in combination, the decisions of which pages to create can be more targeted from a marketing perspective, and this can make a well-ranked site look good instead of just “adjusted”.
The key to this is finding a web designer and an SEO expert that can work well together to make this process seamless. Or else to find an SEO expert that also does web design (as TMO does).
Attention to these details was pointed out by Last Click News.