Many a job has been won or lost based on the character of a prospect. In fact, I've lost count of how many times I've seen otherwise very technically skilled people lose out to basic inter-personal communication. Above all else, a seeming lack of tact.
I do not think developer grading is impossible, but there is so much more context involved. The "score" is dependent not just on the company, but the time and place in the developer's and the companies own life cycle. The perfect fit is always subjective -- these are organic life forms not rigid machines.
That also means the recruiter(s) need to understand the questions they're asking. Technical merit is all well and good, but how well can a recruiter process the answers they're getting? This can't be a bullet point questionnaire with blind matching of answer "C" to question "1". Sometimes solutions aren't so black and white.