Ironically this mirrors the RIAA's argument. They claim that due to a failing CD industry, and lower revenues from online distribution, they should only be charged based on what they earn. Of course, as the artists who are waiting for their cut of the hundreds of millions of dollars collected last year when various online services settled copyright infringement lawsuits can tell you, in the entertainment industry every project officially loses money until the artists' lawyers and accountants prove otherwise.
If the CRB decides to go along with the RIAA proposal they risk a backlash from Congress, who have so far not had the resolve to overturn webcaster royalties through legislation. However, if the RIAA's request is granted they'll effectively be giving CRB critics ammunition.