The ARS report seems to miss that EFI64 is required for Mountain Lion. While a Mac might have a CPU capable of 64-bit, it still might be running EFI32 and therefore won't be supported. No EFI64 means no 64-bit kernel which means no Mountain Lion.
Actually, people seem to think EFI32 is capable of booting a 64 bit kernel. Linux can do it. It's just Apple is being its usual stubborn self; artificially limiting support for machines to try to get people to buy new ones. What's wrong with including a 32 bit kernel with ML? Back in the Classic OS era, machines such as the SE/30 and 6100/60 had 7 years of OS updates. Now we're down to just 4, on an OS that's much more capable of supporting a wide array of hardware.
They dropped all models which do not support at least OpenGL 3.2 core profile. I think this is the main story here. Personally, I welcome this decision.
So why aren't Mac Pros with upgraded GPUs that fully support 3.2 able to run ML? Why is this a welcome decision for you? Does it somehow improve your life?
People can't legitimately expect to receive the newest updates on machines that are 3+ years old.
Why not? As I stated above, in the Classic OS times, you could update machines for 7 years after the purchase date. Even in the PPC OS X era, the machines were supported for longer. Support was dropped for the G3 CPU was because it simply didn't have the features (namely AltiVec) to run the latest OS. The Intel architecture is largely the same between the unsupported and supported models.
First Unibody Macbooks released in 2008 had EFI32 only and yet can still run Mountain Lion.
The first Unibody MacBooks have 64 bit EFI.
Working on the low levels required for hardware access in a driver is where 32bit to 64 bit porting requires the most effort as often you're dealing with fixed width registries and can't simply "recompile" code into a 64 bit binary, you have to adjust types.
That's true, but Apple's ported pretty much all the drivers for the unsupported Macs to 64 bit anyway, as the hardware between the last EFI32 Macs and first EFI64 is almost the same.
There's no reason why Apple can't compile the kernel in 32 bit for the EFI32 Macs, other than the greed to get people buy new Macs. Only thing is, there aren't really enough features in ML to make people upgrade, people'll just stick with SL or Lion as Microsoft experienced with Vista/7, a large proportion stayed on XP.