Are there "standard" methodologies for theming visual sub-sections of a Drupal 7 website? Say your website is "Homewerks" and you have a "Plumbing" sub section (homewerks/plumbing/ - many pages) and a "Floor-coverings" sub-section (homewerks/floor/ - also with many pages). And you need a unique template for all the pages in a sub-section-group - plumbing photo masthead in the plumbing section and so on.
If each of these sections have their own sub-navigation/menus, say located in a side bar, one can just create a unique menu for each section and use something like plumbing/* in the menu setting in conjunction with the page url/path alias and the menus display on the pages related to the proper section.
But attempting to style/template these unique sections, .tpl files only seem able to use internal paths? So you can lock a front/home page to a specific template (page--front.tpl.php) or lock a single page to a single internal path .tpl file (page--node--8.tpl.php). But how do you style an entire group of pages - short of creating a .tpl file for every page in the sub group (not a great idea of course)? And yes - I'm still totally confused by .tpl naming scheme :)
This seems (in any documentation I can find) a glaringly vague and missing part of how the template stuff works. I know there must be lots of ways but isn't there some standard, recommended way to do something so everyday common place? What am I missing?