If I had to guess, it would be that the OS is considered an "enterprise" OS, and that the CPU is too low end, now, to be considered that. It is kind of low end now for even personal use.
Not that people only use the OS for high end server hardware :)
At work, we still have to support 500MHz Pentium IIIs with 128MB of RAM. Hopefully that requirement will be dropped before we migrate to 6. We had to make kernel modifications to even get the PCMCIA support to work on it.