Let me be clear: I support "PCMag's" right to write an article about alternatives to Limewire. It should not be a crime to link to software just because that software can be used to break laws.
That said, my guess is that the vast majority of content available through Limewire is copyrighted and being distributed without permission. Alternatives to Limewire are "of interest to your readers" because they're looking for new places to download this copyrighted content. In my experience the average person running Limewire almost certainly needs the help of more experienced people--like technical journalists--to find good alternatives to Limewire. So it seems to me that PCMag is providing a valuable service to many people who would like to download copyrighted content.
Sure, if PCMag didn't write an article about "alternatives to Limewire," someone else would (albeit maybe someone with different interests in mind, or someone with worse SEO skills). Sure, when presented with a letter like this I can see why they choose to try and get out in front of this issue. Sure, there may be legal implications to reacting in any other way than the way they did. Nonetheless I think their statement offends my sense of frankness and honesty.