That's a nice description of what's going on, but it really boils down to:
* Running 32-bit kernel on 32-bit hardware
* Running 32-bit kernel (mostly; enough that kexts are 32-bit) on 64-bit hardware
* Running 64-bit kernel on 64-bit hardware
Interestingly, for a while only the Xserve defaulted the kernel to 64-bit mode, whereas all consumer machines used the 32-bit kernel mode, though this could be toggled using a certain keyboard chord at startup (I think it was holding down 6 and 4). Eventually this shifted so the 64-bit kernel became the default, but only after giving kext authors enough warning so they could update their kexts.
In any case, as diverting as this is, it doesn't really matter to the consumer. There was only one version of OS X to install, and it ran in whatever mode was appropriate for the machine in question. The only reason consumers ever had to care what mode their kernel was running in was if they wanted to use a kext that did not have both 32-bit and 64-bit support, and by the time the kernel switched to 64-bit mode by default, this was pretty rare.
* Running 32-bit kernel on 32-bit hardware
* Running 32-bit kernel (mostly; enough that kexts are 32-bit) on 64-bit hardware
* Running 64-bit kernel on 64-bit hardware
Interestingly, for a while only the Xserve defaulted the kernel to 64-bit mode, whereas all consumer machines used the 32-bit kernel mode, though this could be toggled using a certain keyboard chord at startup (I think it was holding down 6 and 4). Eventually this shifted so the 64-bit kernel became the default, but only after giving kext authors enough warning so they could update their kexts.
In any case, as diverting as this is, it doesn't really matter to the consumer. There was only one version of OS X to install, and it ran in whatever mode was appropriate for the machine in question. The only reason consumers ever had to care what mode their kernel was running in was if they wanted to use a kext that did not have both 32-bit and 64-bit support, and by the time the kernel switched to 64-bit mode by default, this was pretty rare.