Do People On Y!A Have A Misguided View Of What Is "Underground"?

This is a follow up to my last question. It seems that people on here think underground is a persona and a sound rather than about how much the record sells. For example. You probably would consider OC - Jewelz to be a mainstream album. Yet you would probably consider Aesop Rock - None Shall P to be an underground album. Well Jewelz peaked at number 90 on the Billboard 200 and None Shall P debuted at number 50 on the Billboard 200 selling 13,000 copies in its first week. Bazooka Tooth sold 20,000 in 3 weeks. Fantastic Damage sold 50,000 in a little over a year. Can Def Jux rappers really be considered underground if they are making these kinds of record sales?