Ignition Key Slot vs Hole

General Motors will rework or replace the ignition keys on about 3.16 million 2000 to 2014 model year cars in the U.S. because the ignition switch may inadvertently move out of the “run” position if the key is carrying extra weight and experiences some jarring event.
The use of a key with a hole, rather than a slotted key, addresses the concern of unintended key rotation due to a jarring road event, such as striking a pothole or crossing railroad tracks.
Only one of the models included in the U.S. recall of 3,160,725 cars is still in production – the previous generation Chevrolet Impala, which is sold to daily rental fleets as the Impala Limited. The total North America population – U.S., Canada, Mexico and exports – is 3,360,555.
The safety recall follows a review of ignition issues following the recall in February of 2.6 million Chevrolet Cobalts and other small cars. GM is aware of eight crashes and six injuries related to this recall.
If the ignition switch moves out of the “run” position, there is an effect on power steering and power braking. In addition, the timing of the key movement out of the “run” position, relative to the activation of the sensing algorithm of the crash event, may result in the air bags not deploying.
Source: GM