Repeated Failure To Adequately Shield Internal Components From External Stresses
Apple has demonstrated a repeated incapability to correctly engineer casing in their plasic-body laptops over many years. They appear to have solved this issue by essentially giving up and just unibodying everything.
The iBook G4 is liable to stop working due to the failure of the casing to protect the motherboard from external stresses. This leads to a modal fault: The pins of a small chip attached to the motherboard come away from the motherboard, preventing the laptop from booting. See coreyarnold.org.
Some models of plastic-body MacBooks suffer from an issue whereby the integrated webcam will stop working, with perhaps intermittent returns of functionality. This appears to be due to (once again) the failure of the casing to adequately insulate internal components from external stresses. This results in stress on an internal cable connecting the webcam, causing it to become disconnected.