They are meant to be supplemental, acknowledging that we don't have things as well documented in text as we would like we made the developer walk through series of videos to show step by step how to build a feature and keep your code separate from mojoPortal. Of course things change over time so even the videos are not comprehensive or completely up to date. If you find anything contradictory and are unsure of specific things feel free to ask in the forums.
In general for experienced developers the source code itself is the most complete and comprehensive documentation available. The way the mojoPortal.Features.* and WebStore.* projects are organized and implemented is exactly how others should develop their own features and serves as a good model of how to structure your projects. And learning how any particular feature works or at least how it plugs into a CMS page and how it can have linked supporting pages is what any developer really needs to know for developing custom features.
Hope that helps,
Joe