Even if a Kerry ad directed toward a journalist influences 100 regular people, their influence is still out numbered by the vast number of average Americans. Plus, that's running on the assumption that everyone is going to vote the way that Kerry and the "influenced journalist" tells them to.
So what? Does it really matter if there are only 1000 journalists out there?
If the MSM "journalist" in the national press corpse shows words, summaries, and attitudes and inflections (from a supposedly "unbiased" reliable source!) to twenty million people for free, then your "ad" has bought incredible leverage in the voting public that tries to be "well-informed"!