Have you considered an option where he's something like a college student who needs to move around a bit? Or perhaps he's a programmer/developer and sometimes he needs to do stuff on the go. (same can be applied to photo/video editing and other workloads. Not terribly common, but it happens).
I agree that a desktop is usually the better solution, both by price and by convenience, but sometimes you need both mobility and power, and then your ony option is a powerful laptop.