Why would there be a need for a publisher? Where is the problem for Microsoft to just host the game on their servers, let people buy it off XBLA, keep a certain percentage of the money and forward the rest to the developers?
It just seems like Microsoft said "Our personal pipes are full, but maybe one of our licensed partners has some bandwidth for this game." Extrapolating on the headline, it sounds like Microsoft's pipes are full of Xbox exclusive titles. Preferring exclusives seems like a reasonable general guideline when there are simply too many games worth investing in. This is especially true for simultaneous development of cross-platform games. Microsoft certainly wouldn't want to spend time and money waiting on or helping a studio finish up the Playstation 3 port of their game (PS3 development always takes longer).