They've been creeping that way for years.. the old Wolfenstein needed 8GB, Rage needed 25GB, Call of Duty: Ghosts needs 40GB, so yes, the demands for 'HD' definition is the cause. It'll get even 'worse' if 4k screens ever really take off - at that point developers really are going to have to take a seriously look into procedural textures and materials (it could be argued we're already at a point where that needs to be happening).