I don't think you're missing anything, but I think you (as many have before) are forgetting about one of Rails earliest and biggest selling points: curation of best practices for creating specific kinds of applications. While the ease with which skilled practitioners can configure the framework to work well for an API-driven application is a testament to its flexibility, the out-of-the-box conventions have been in need of some love for awhile.

I don't think this is a huge deal, but it will definitely be nice to have official support for this configuration.