I don't look at the About Mac window all the time, but it is not the same as everyone else's. I managed to remove it before (not through editing any files or system files etc) but simply disappeared somehow. Now it is back.
Yes, I have changed the Startup Disk and have 1 thing listed but it still appears in the About Mac window. My About Mac window looks normal, but with 1 extra line,
For example:
Processor: 1.5GHz PowerPC G4
Memory: 512MB DDR SDRAM
Startup Disk: Macintosh HD
I did not have that listed before, but now I do. I have reinstalled a few times and have restarted many times, even holding down option (alt) to change the startup disk to the same Macintosh HD, but it is still the same in About Mac.