I firmly believe this is simply marketing sneaking into your games unnoticed.
Like the games that used to be on your mobile phone. Solitaire, minesweeper or whatever.
The last phone I bought had no games, it had 30 second demos and a link to the site where I could go and purchase solitaire, with actual money.
As for the multiplayer issue;
4-player splitscreen is 1 copy sold. No splitscreen probably isn't 4 copies sold, but at least it will be more than 1. Also, everyone playing the game will have paid the full price.
Eventually, we will grow accustomed enough to online play that it becomes a necessity in gaming. Which will be the point where the price of your subscription is tripled.
Other than the income thing, it's also a piracy thing. Forcing people to play online effectively forces them to actually buy the game, or go through a lot of trouble getting the latest "untraceable" console mod that could get your account banned the second the next update hits.
The fact that it took this thread for a lot of people to realise "Hey wait, splitscreen is gone" already shows how much a lot of people really care.
I'll bet the vast majority of gamers (that aren't sharing a console) only own 1 controller per system, except for their Wii perhaps.
Any possible second controller was either given to them for free, is a collectible, or is commonly extremely busy collecting dust.