More than simply Domain knowledge, I feel it helps significantly when an Architect has some level of business savvy. To some degree I suppose this encapsulates a level of social grace, though I don't know that acquiring those soft skills is the point of having a "head for business".
Sometimes an architectural decision can be made that is perfectly sound from a technical perspective and it even seems to fit the business needs - those needs, as stated by the business, often carry an implied level of knowledge that isn't captured in a requirements document or visible as an artifact of the business itself. There is a reason why the perception of IT project failure rates hovers in the 50% range at any given time, and I wouldn't be surprised if this has something to due with the that lack of "insider knowledge" and general understanding of business exhibited by some Architects.
