Yeah, it is really just a setting from what I understand. Clocks and memory bandwidth are lower in handheld mode and higher in the dock due to increased power. Really isn't about the dock though. That's my understanding anyway.
The GPU doesn't change when docked. It just has more power. So it could probably output at higher resolutions without the dock, but it would require more juice from the battery and wouldn't last long. Switch controls all of this though and only toggles the higher resolutions when docked. Makes sense considering the built in display can't go higher than 1080p anyway.
Other handhelds have controls available to change the wattage and resolution whenever they want whether docked or not. I can plug my Legon Go S undocked into my TV at play at higher resolutions but again, it won't last very long.