While it could be said that nothing is fair in love, war and business, I, personally, find unethical business practices to be quite loathsome. Sometimes a company that tries to win through intimidation and questionable legal threats deserves to have the world know what they're up to.
My grandmother once gave me a piece of advice that's stuck with me- "Integrity is doing the right thing, even if nobody is watching." Years later, I think about that and I wonder, how many people are running their businesses with a smile on their face and a knife behind their back.
So yeah, there are plenty of times where airing dirty laundry is a shallow thing to do, but there are also times where you can finally see the true colors of a company and what they really stand for.
If someone like WP or another company is going to send a letter like this, they should operate on the assumption that it will be made public (especially if it might later end up in litigation.) That would seem to just be good practice with any document you're issuing outside of your company, especially when you're basically initiating a disagreement.
edit: Yep, sorry, I was not clear, the kind of chuckling one does when a business freely publicizes an act of stupidity that could cost them customers.