Very well said about the internet bandwidth guys. Good points made here. I'd like to add something if I may. The guys that make the PS3 possible and PS4 possible, etc. also look at the global market, not just single country markets. As this technology gets cheaper, it becomes more widely available.
Now say if Verizon was to offer unlimited bandwidth and very fast and cheap download speeds, downloading complete games would be very convenient. However, when you compare that so say Senegal, there may be very limited internet bandwidth provided, and the speeds may not be as advanced (amongst other things) so it is more profitable/ logical to go with disc drives. (or as might be seen, both) Selling consoles is not only a business for profit, but a way to bring the people of the world together.
You can't make a system specifically for one group of people because it eliminates the possibility of connecting to other groups. Communication is vital in this ever modernizing world. Just my two cents. Hope it made some sense.