They are hoping that by releasing a large chunk of the game as a demo, players will be hooked by everything it has to offer and then they'll buy it. (ps3attitude.com)
The downside of digital content is that a good chunk of games now require internet access. (averagexboxgamer.com)
For a huge chunk of the game of the game you will be running around and doing does same actions as countless enemies are thrown at you. (xboxexclusive.com)