Actually I talked to MadSkillz online a few nights ago as he was downloading his review copy of the title. Not going to relate the conversation verbatim, but he seemed pretty confident that this was how Microsoft intended to release the majority of their review copies in the future. It isn't even unheard of he gets download only copies of software all of the time. It is looking like this is the way reviewing will be headed. You can see the advantages against say lost in the mail, or pirated prior to release.
That isn't to say that Microsoft or other developers are going to stop sending out gift baskets to the priority outlets. Though most involved probably aren't going to be shipping out hundreds of physical copies of games in the future. Anyway I hope that answers your question. As to why it happened. As to whether Microsoft is going to open up digital download on day one of release. I seriously doubt that they will. There are so many reasons to not do that. Primary among them is the very real problem with modder theft, and that millions of people trying to download full games simultaneously would probably cause real technical headaches. They can release them later when the demand is smaller, and they don't want to make more production runs. So yeah you will probably be able to download this game in a years time, but first they are going to run through the physical media.
P.S. Oh and if you happen to run into MadSkillz online give the guy some love. He surely does need some of that. He had a major medical calamity last month. He very nearly died, and is still recovering from the trauma. Even a little emotional support goes a long way.
