Not everyone is an audiophile, personally I think sound cards are silly. My board allows me to use my 5.1 $120 speakers, as well as my headset with mic, words are clear, audio is audible... Would a sound card help $120 speakers? Probably not. Would I invest in a high end sound system for my computer? Probably not. Therefore do I need a PC with two sound cards? Probably not.
Different strokes for different folks.