I think the problem is not the accuracy of the sensors themselves but that its difficult to have a placement inside the car such that the measurement is minimally influenced. Many factors influence temperature: heat from the motor, from heating and from the sun shining on the car and perhaps others.
And it also depends what exactly you want to measure: air, motor or inside temperature? People might get confused. And inside temperature might differ a lot: behind the windscreen it might be a lot hotter than at the floor.