This quote on a blog post summarizes part of the underlying design philosophy for Kete's relatively flat organizational structure.

It's important to note that as of Kete 1.2, Kete CAN have infinite depth navigational structure through hierarchical values through an Extended Field (e.g. setting up a "categories" field with choices that include top level categories and an arbitrary number of levels of subcategories). However, the usefulness to end users is highly dependent on your site's audience.