PROPOSED CHANGE (2/10/13): Eliminate rule 10.3 and add ground clearance ruling: The minimum ground clearance is to be judged by the cars ability to roll over a 2x2 board that is milled to be 1 ½ x 1 ½.
There were reported problems and delays at races where cars took out timing wires at finish lines. There is also a safety consideration as some car designs experienced loss of steering or braking when nose cone was down. This will also provide inspectors and builders with a more uniform tangible device to ensure compliance.
I think the concern addressed by 10.3 is the danger that a tire might come off the rim at speed and the lowest point of the vehicle dig in and cause a flip. Different tires have different side wall heights. For example, if you have a tire with a three inch side wall, an inch and a half ride height will not help you. I think 10.3 is more effective as is than setting a stock ride height.