It's even more exaggerated than that. So-called patent trolls are not generally interested in shutting down infringers (unless they have an exclusive license with someone else, which I don't think Personal Audio does). They want infringers to stay in business so they can get paid licensing fees. Since they want to maximize their revenue, they don't even want the license to be so burdensome that infringers simply close up shop rather than pay. What's more, the normal standard for patent damages is a reasonable royalty, so in most cases the patentee can't even ask for (much less receive) enough damages to shut down infringers.