I think there may sort of be another thing going on: Basically, that the length of load time is an indicator, "This is a really serious program." I've sort of noticed the same thing with test machines: the more expensive the machine, the longer it takes to actually get to the grub prompt.

Six minutes is probably excessive, but having GTA take 1-2 minutes to load almost certainly makes people feel better about the money they spent on the game than if it loaded up in 5 seconds like some low-production 2D adventure game.