It's all about SEO. People that use WordPress or other mainstream blogging software usually have a lot of options when it comes to plug-ins. Storefronts and non-templated websites have a lot more work to do to receive the same results.
Google has a formula that is far too complex for my head, but it includes things like: amount of times phrase is published (both visible and not visible), frequency of updates, amount of hyperlinks (the reason why Wikipedia is the first hit for just about anything), etc...
Many large online storefronts pay people (a lot of money) to get their results first... as we all know few of us have patience to go to page 2.