What's in a metric?

There was a brief article in today's New York Times about the lack of a reliable metric for determining Hulu's online audience.  The Times kindly calls the indeterminate audience count "imprecise", but it cites a range of 8.9 million (Nielson) to 42 million (comScore) for March 2009.  Such a spread indicates that data is not just imprecise, it's bordering on useless; this is particularly the case since this audience count is needed to drive Hulu's programming decisions as well as advertisers' spending decisions.

How is it possible that such wild variations in reporting are possible when there are established standards for measurements?  Is it simply because, as a marketing sub-field, online video advertisements have yet to be properly standardized?

Hulu is a big website with major corporate interests.  What I find more perturbing, then, is the mapping of this issue of underdeveloped metrics on to smaller companies and organizations.  What does such a business do when it knows that it wants a greater online presence but it also has an extremely tight marketing budget?  It undoubtedly becomes harder for that business to justify the spending on online media and search marketing when even the big counting firms can't seem to be in agreement about what constitutes unique visitorship and audience size.  I don't think that this uncertainty warrants the extreme conservatism of not spending on online marketing at all; I do think, though, that the uncertainty results in exponentially larger amounts of risk -- proportionally speaking -- for the smaller businesses who are just interested in getting their small share of the pie.