For an automotive ECU that sees engine vibration and thermal cycling, that reliability margin saves a field-return investigation.
That is the cabin and engine-bay ambient for most passenger vehicles — a body controller or a CAN gateway clocked at 27 MHz stays within spec through a cold crank and a hot soak. The ±10 ppm frequency stability holds across that entire temperature band, so the bus timing budget doesn't need extra margin for temperature drift.
