For example my brand new Hyundai Sonata has pretty shitty rear visibility due to it's 'sleek' styling and therefore smallish rear window. I could cite many more.
It's more than the mirrors, and unless you have transparent pillars on top of the car (giving up the structural integrity of the cabin) it's going to have blind spots.
You should actually have them a lot farther out such that visibility in your side mirror coincides with losing rear-view visibility. That position is a lot farther out than most people think and is tricky to do the first few times.