Not necessarily. In many sealed-bid auctions, bidders hope to win with a lower bid (often much lower) than they would if they were bidding against others in the same room. This is especially true if you have no idea whether anyone else is bidding on the item at all. I have placed very low bids on items in sealed-bid auctions for things I had no immediate need for, but would happily pay for if the cost was very low (and I have won many such items, sometimes because no one else even bid on them).