This isn't the first time for that tactic. Some people are suing a gun manufacturer. Exact same logic (or lack thereof) applied there.
Guns have just one purpose though. I believe blog software is a tad different.
Yeah, suing gun companies for specific murders is also stupid, but the analogy isn't that strong.
Guns can be used only for killing/injuring people. I haven't heard of anyone using a revolver to generate power. (Yeah I know the line "you have guns to deter others, not to actually use them." and I know the second amendment's advertised raison d'etre. But I don't believe everything I hear).
Blog software also has one purpose, but it is not crime related (at least assuming we have freedom of expression). The link between blog software and piracy is not as direct as the link between gun and murder.
But again, suing gun companies for murders is stupid.