Dont think its the frequency. I would say its the detail. The life and breath of the music.
Besides, many budget cartridges only respond to 20 hz anyways. So you dont really have to worry. 20hz is pretty damn low anyways. So unless you got speakers that can handle it, then there's no point. In fact...lots of subwoofers dont even handle down to 20hz. I guess we shouldnt really call them subwoofers then eh?

Being a newbie in this field, the information here could be inaccurate, but I hope it is.