**plone.namedfile** [is a dependency of **Products.TinyMCE**](https://github.com/plone/Products.TinyMCE/blob/master/setup.py#L35); so, even if we don't install **plone.app.dexterity** we will have it in Plone.

I think we are just interested on checking if **plone.app.dexterity** is installed or not.