You may be trying to interpret the numbers as scientific, when in fact they are simply a gauge.  And I believe Steve is right.... Neilson is a well respected gauge.  And in the end result its not what you, or I, or even Steve thinks... its a gauge that advertisers use to determine what to pay for their ads to display on those screens.  There is an old saying about using a broken ruler to measure anything... if the same broken ruler is used to measure 2 different things... the relationship to any difference will be correct.  The point is... does it really matter if 10 million see the material, or if 20 million see the material... its still a big number, and much bigger than if the same material were to be run on the local evening news broadcast.

Do I think every customer will see VU material... of course not, however I think it would be a fair statement to say that if the viewing estimate were even 1/2 correct, or even only 10% correct... the same would hold true for the percentage of viewers on any other medium as well.