This isn't completely correct. It does work if the counter-suit claims are valid and encompassing - sanctions in the legal process can provide significant leverage, especially because the "patent-trolls" are heavily involved with patent attorneys.
"Reback often tells the story of how a team of IBM patent lawyers went to Sun Microsystems Inc. in the 1980s and claimed that the then start-up was infringing on seven of its patents. After Sun engineers explained why they were not infringing, the IBM lawyers responded that with 10,000 patents, they would be sure to find some infringement somewhere." -- The Washington Post
With patent trolls maybe you could counter-sue for tortious interference, but that's a pretty hard one to make stick, or you could get a judgment rendered that requires them to pay your fees if the suit is totally ludicrous, but I'm not sure I've ever heard of that happening in any kind of patent lawsuit.