Words in the url's are only one part of SEO. You have to get all the other parts right in order to do well on the search engines. I personally am a master at SEO for vBulletin, and am working my way through issues specific for zencart.

Definition of SEO

What I call the Three Secret Steps
  1. Search phrase selection
  2. header tags
  3. content


Pick the search phrases that you stand a chance at ranking for and that are receiving traffic

Get the title and meta description right

Get an h1 and intro paragraph including the search phrases for each page.

See my site for more details on Zencart SEO work in progress