Traction Verticals

If you'll permit a minor bit of information architecture geekery, I think this list could be thickened out substantially into a hub about traction with a spoke about each "traction vertical" (I suggest rebranding that into something more instantly comprehensible). Then you could go into substantial detail about each without totally overwhelming the visitor. Think of the classic wiki structure (tiers with reference nodes and progressively detailed leaf nodes, with interlinks where appropriate), although it doesn't have to be a wiki.

For example, SEO is a pretty deep topic, and there are facets within facets and multiple competing approaches to it. Rand Fishkin and the guys at SEOMoz do great SEO, but they tend to use a different bag of tricks than I do. You can better do the compare/contrast thing if you're not trying to encompass the entire subject of online marketing on a single page.