Steve,
if you have a look at other CMS on .Net, you will notice similar features, URL rewriting is a common requirement (for users and search engines).
DNN is currently based on Web Forms, meaning that all modules and elements are web controls on the server (except a few modules using MVVM pattern and JS on the client side).
The page structure is stored in the database (table tabs), so are module instances (table Modules, linked to tabs using TabModulesTables). ModuleDefinition is the link to the module controls with a link to the source code files.

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Cheers from Germany,
Sebastian Leupold

   

Speed up your DNN Websites with TurboDNN

Steve,
I agree, that DNN is more than a CMS - I would call it a platform for solution development, and I know a number of integrators and software vendors, using it accordingly.
If you focused before on ASP.Net WebForms, DNN will be a good option to start - to improve your options while focusing on the business case of your clients instead of hassling with problems, others solved already.

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Cheers from Germany,
Sebastian Leupold

   

Speed up your DNN Websites with TurboDNN