I'm not sure I get "Pre-Orders". Consequently I usually don't do them, regardless of special digital trinkets thrown in or not. In this day and age where most games are starting to go to digital download, it's not like the game store down the street is going to be running out of copies..
Pre-Orders help everyone in the supply chain (developers, publishers, suppliers, retailers, etc) estimate the demand for something and, in the case of digital distribution, some capital up front to work with.
By helping them anticipate demand and supply cash, they offer rewards to try to entice you into their data/cash pool.