I was a bit annoyed when I first realised that you couldn't play two player Wii boxing with what was in the box. Nintendo must have planned it this way, as one of the first thing people buy for their Wii is an extra set of controllers. This explains why Wii Play is out of stock almost everywhere. This game has been a top seller since day one because of the free remote control included with the game.
Not strictly true. Some consoles in the past like the NES, SNES and even PS2 have come with two controllers but these are in most cases special packs or editions.
However it is much more common to only have one controller in the box which is the norm. Anyone who want's or excpects more then one is expecting too much since one controller is the norm generally speaking.
The main reason why only one controller is included is because the profit margin on the console is next to nothing and most profit is made on the accessories and software. Nintendo probably can't be excused for this as the controllers cost next to nothing to make and they do make a healthy profit on each Wii sold.