People are so used to seeing "20-20,000Hz" everywhere they expect their speakers to go down to 20Hz. And you are correct that *real* musical instruments - string basses, contrabassoons, tubas, timpani, etc. are well in the range that the Heresy reproduces. One notable exception would be a pipe organ. It would be hard pressed for any speaker to reproduce a 32-ft length pipe resonating.
When anyone says the Heresy has weak bass, I just play a well-recorded classical piece with an ff hit on the bass drum and that's that. The first movement of Copland's third symphony or the third movement of a Tchaikovsky 6th would do. It's extremely tight bass with absolutely no boom.
Now if you're a rap/hip-hop fan, those are artificial bass notes created by a synthesizer/drum machine. A computer can generate a waveform of almost any frequency, but they are not natural musical instruments. For that, just get a powerful subwoofer.