Seatbelts and W & B
Mudskipper, yep they have special seatbelts that can be worn when lying down on these things.
Artificial Horizon - i guess they've done the numbers. If 33 seats sell for half price then there's no weight on those seats.. 33 x 80kg (approx per person) 2640 kg. I fly bug smashers so just passing on info i've heard. a 777 which wants to carry an extra ton of fuel on a long haul needs to carry another tonne to burn because he's carrying that first ton. so if they're carrying 2.64 ton less because of those 33 seats then they can carry less fuel due to reduced payload and less fuel again because of the reduced need to carry the fuel in the first place. bit confusing but i think you get the idea.
my two cents re: skycouches. stupid. i'd rather spend the money when i get there..