Well yes, I know that when our avatars are disrobed, they are wearing underwear.
But what I meant (and what I thought he was talking about) was why bother buying underwear to put on?
Quite technically speaking, you're not really wearing underwear if you don't use any that you bought.
Unless you want to make an outfit made of things normally considered undergarments, you don't even need to buy underwear from the shops.
(I hope that all made sense. Now that I go back over it, I'm not quite sure it did, but my brain's half fried with heat)