Actually pre-ordering can make even more sense in the digital era than it did in the CD era. With Steam if you pre-order you can sometimes download early or it starts the download automatically ASAP so that when you want to play it on release day you can simply click play rather than think "oh I want this, lets buy it" and then wait hours for it to download and install.
If you had to leave your house to buy the disc and come back and install it then you had to do that whether you pre-ordered or not.