It's possible (although I have no idea how plausible) that Mr Balasubramani could have written that letter pro bono, which would be excellent advertising given the coverage this is getting, and since he's on the Good Team, it's probably more valuable publicity than that of the other fellow.

I speculate (at the risk of demonstrating my ignorance) that this letter, at 1 page of background and ~4 pages of analysis, may not actually have taken all that long to prepare, especially for someone with intimate knowledge of DMCA and libel/defamation case-law.

Of course, it's a lot more complicated if he has arranged representation rather than just letter-writing, and the contact telephone at the end perhaps suggests he has, so it's quite possible I'm wrong.