That is like claiming a tool like lint can't be used to catch bugs. And... not all of them are. Did you read all of the tools in the "mixed languages" section? Quite a few of the really good tools can find mistakes in dynamic languages.

Shit, this is no different than the article making the rounds talking about the many "gotchas" in bash scripting. Just making a tool that spots those is likely to catch and help correct errors.