WHY buy a extended Warranty as they dont honour it

I purchased a Acer Laptop through Mustek Durban with a 3 Year Extended Warranty. After the suppliers warranty expired the MUSTEK extended warranty takes over. I sent the laptop into there sevice centre as the left hinge packed up. They have now informed me that this is physical damage. I have questioned it and they stil refuse to see the point.- if a hinge a part of the working mechanics of the laptop and has stopped working why is it physical damage. The laptop has never been dropped so how can they claim they the cause of hinge malfunctioning is physical damage. If you go to the Acer fourm there are complaints about the same issue- left hinge splitting casing . After numerous emails they have refused to accept that this is a manufactures fault and still rule physical Damage. This is unacceptable as what is covered in the extended warranty and why sell you an extended warranty if they don't honour it. I enquired on-line and the left hinge to import to South Africa will cost R200. The quote I got was in the region of R1700. This is the last time I purchase from MUSTEK. They just don't care about their customers and hide behind politics