I think a big part of the enjoyment comes from the feeling of ownership and achievement in everything you build. You have to work to get all that stone to build your house, and you have to build it yourself, brick by brick. You have to dig miles of tunnels to find those rare ores. Also, you actually have something to show for all the work you've done, something you can use. If you're playing survival, it's a fort that will protect you from your enemies. The third panel of this recent PA comic really sums that feeling: http://www.penny-arcade.com/comic/2010/9/20/