Lack of storage space on their main SKU is what is stopping them from doing that at the moment. That and the fact that one of their other SKUs does not come with an HDD right out of the box as well. Once the 60GB model comes out, I am willing to bet that they will start distributing some of their games over Live.
And by the way, they are already "distributing" other things over live. Xbox original games, Xbox Live Arcade, DLC... so on and so forth. The only thing that they AREN'T doing is offering full scale current gen games.







