Dear 93tid,
you may also be not entirely correct, there are many chairs with only one leg, quite stable! And a chair with only three legs are often less stable than the ones with four.
What you might want to state that flat surfaces are already defined by three points.
Nevertheless a cross platform framework, with only three pillars is less intriguing than the one with more pillars.
Mobile platform is definitely one which would make it unquestionably stronger.