I am concerned over loss of ownership of your games. The difference between steam and Xbox is they are not going to put out a steam 2 in a few years and make all my previous games obsolete. If I want to play one of my older PC Games I am confident I can always load up steam reinstall the game and it will be there. That is why I will compromise with steam and not Xbox on those issues. Plus steam sales.
In addition to that being able to loan a game or trade a game with my real life friends is important to me. I have gifted a lot of my extra copies of games I get on steam to them and vice versa. I do not trust Microsoft to give me extra copies of games that I can give out. They can potentially earn that trust but it will take time and consoles have a life cycle.