Why does the xbox last longer than...?

The xbox that built and ready for kinect? Because I still have my working xbox that I bout in 2008 and my xbox built for kinect that I got in 2010 May 24th only lasted till January 28th 2011 and I sent it to Microsoft to get it repaird and when it arrived after three months it didn't want to read the game disk that I put in so I'm waiting for my xbox to come Back from the Microsoft network from being repaird and My 2008 xbox is still working fine?