Originally Posted by Misa
If Apple is dropping support for some 64-bit Mac's, it's probably has to do entirely with the Video or CPU features. Like they're probably dropping support for the systems that can't do OpenGL.
The White iMac's have GMA, Radeon 1600(OpenCL added during the 4000 series) or Geforce 7300GT (OpenCL was added during the 8600M series) but this doesn't exactly make sense since the ATI models in the next set of iMac's are the ATI 2600HD, and don't support OpenCL either.
The other possibility that came to mind was Intel VT-x support for hardware assisted sandboxing or something, but the C2D polycarbonite iMac's have C2D's that support this.
So in looking at the cut offs...
iMac (mid 2007 or later)
- Has HD2600 or better
MacBook (13-inch Aluminum, 2008), (13-inch, Early 2009 or later)
Has Geforce 9400M or better
MacBook Pro (13-inch, Mid-2009 or later), (15-inch, 2.4/2.2 GHz), (17-inch, Late 2007 or later) are all models with the Geforce 9400M or better (assuming intel's video isn't laughable)
MacBook Air (Late 2008 or later) - Are Geforce 9400M or better
Mac Mini (Early 2009 or later) - Geforce 9400M or better
Mac Pro (Early 2008 or later) - Radeon HD 2600 XT or better
Xserve (Early 2009) , no idea.
So all that's been established is that only the models using Geforce 9400M or Radeon HD2600 are supported (or the HD Graphics that are part of the Core i5/i7 series)
Though it seems that if it was for OpenCL, that doesn't quite fit. The only fitting answer is that they don't want to support the GMA and any GPU older than the Geforce 9400M and Radeon HD2600