One word; Abuse. (intentional or not).There are so many people here complaining that their 2009/2010 MBPs are "on their last legs" (learning a new expression every day). How can that be if they are supposed to be of a high quality build?
"Last legs" is a relative term. To me, any Apple product that has earned this label is at least still functioning pretty much normally. I have a closet full of Dells, Toshiba's and HP's that never seemed to have any "legs" at all and died abruptly. R.I.P.