I recently played a few hours of Mario Kart 64 (yep, dusted of the old N64) on a couch with some friends and by the end of it, my lower back was killing me. I never get this when I spend 4 hours playing Civ IV.
Absolutely. If you look at the posture of someone playing a console game, you will see an arched back, pressure on the lumbar, neck pulled back, often feet not flat on the floor.
As you can see from this photo of me playing WoW, PC gaming provides a much more healthy posture: