That's kind of a broad generalization with regard to the auction houses and their clientele. It's true that there a lot of domainers lurking on those sites, but there are also a lot of amateurs (and I don't mean that in a denigrating way). If there is no charge to list a name (a lot of the houses just charge a percentage of any sale that actually occurs) it doesn't really hurt to list your names there (just make sure you understand each one's rules as far as sales types, how offer and counter offers work, etc.
I would also add godaddy auction to the list if you want to get more eyeballs on your names for sale.
peace.
gregs.