Well they're all semi-work related and he doesn't skimp when it comes to that.
One is for his office computer, one for at home, that he can use when working from home and also if for whatever reason the office computer breaks he has a backup, and the last one for his son, who does do work for him sometimes. That's the main reason he went with the nVidia card in fact and that's because Photoshop makes use of the Cuda API's for certain things.
*Edit*
I should also mention that both him and his son are coming from using Apple computers. My cousin had an iMac before that, and my uncle was using PowerMacs at the office but this time around when he was pricing things out he realized he could get a system almost twice as fast for 2/3 of the cost.