Try to divorce your love of Tesla and the green movement for a second and see if this makes sense. Do we really want a giant screen to distract us from the task of driving, now you might have heard "studies" about how it doesn't but think about it, would anyone admit to being distracted while driving that caused an accident? How can you prove this...very difficult. Most drivers would probably take blame for this because of their love of Tesla.
Having buttons and nobs might be old school but it's more tactile and often allows you to keep your focus on the road knowing exactly where the volume button is, or the sunroof. Having a giant screen forces you to look at the screen, tap several times to get to your location, then tap or slide your finger on a precise location, or tap multiple times to adjust volume or setting. With buttons its a push or turn for the same task, having a giant screen could take several more steps taking your attention away from the road.
It doesn't take much to cause an accident, a young child darting out onto the road, a driver running a red light. Most of the demos are done while the cars are stationary, if you're a passenger would you feel at ease knowing the driver's attention is not on the road? worse if the driver's alone he'll have a higher chance of an accident, at least if you're a passenger you can help.
I understand it's more convenient to have a computer to control all aspects of the car, having over the air updates to add additional features is great, I'm glad the Tesla S is the safest car ever tested because somehow I have a feeling it's going to need to be one day for some unlucky owner.