I believe that what is happening is that every plugin has an ‘engine’ - wrapped like a car in a ‘body’ - the user interface. So for each plugin - there is a single car - engine and interface.
Topaz Studio could be imagined as a multi-engined car - just the one user interface - you just swap out the plugin/engine each time.
The use of one, single interface - but a multitude of plugins - allows the user interface extra enhancements, which is where the Adjustments and Community sections come in. The ‘body’ is super enhanced - supplementing and complementing each plugin, giving it extra power and facility.
So the traditional engine from each of the old, standard and much loved plugins is still there - just given a shiny new and expanded wrapper or interface - one interface for all plugins - instead of one interface for each plugin.
So now there is time saved in not having to close one interface and re-open yet another: you can (eventually) apply all plugins from inside the one and only interface which is Studio. That also allows you to make custom presets across all the plugins - something from Clarity, something from Adjust, something from Detail, something from Impression… a myriad combinations in one, convenient, self-made preset.