True, though the main problem with selling goods like T-shirts and hats is the per unit net on them. You just have to sell a bazillion of them to make it worth it.
In WinCustomize's case, like T-Man said, it wasn't launched with the view that it needed to generate any revenue since it would be a skin repository for the community. But as the cost of having it increased and increased, it slowly became more and more necessary for the site to be able to generate enough revenue to pay for its bandwidth and eventually the IT costs.
So in our case, we have it a bit easier since we're not looking for WinCustomize to be a "profit center". If you're looking to have your site be an actual business, then things get much tougher.