Based on years of reading WebmasterWorld and other forums, this resonates with a general sentiment among advertisers – they want to have more control over where their ads go. In particular, many do not want their ads displayed on the AdSense network, because it is believed to be of low quality. At best, ads convert much less (and for less money); at worst, advertisers lose money due to fraudulent clicking.
One could say the plaintiff is being lame for not realizing that one needs to fill out the form in a specific way. (FWIW, I don't know offhand if Google has actually documented clearly.) As a counterargument, there is a precedent for the empty field implying zero, e.g. in using Intuit's online tax prep software.