Why would they cut it off after 1 or 2 releases of OS X? Their install base won't be over 50% in 3 years, it would just be stupid for them in a profit view. Unless the older system's can't handle these next releases. But Apple hasn't done that yet systems that are 5 years old can run tiger. I doubt they will have quad-prosesser, or Xserve systems not being able to run an OS in 3 years these systems.