Tires with stiff sidewalls ride poorly when underinflated. Good tires don't suffer as much. But of course, you need stiff sidewalls if you're going to carry a lot of weight.

When inflating presta valves, removing the pump causes air to make a sound, but that's all coming from the pump. With schrader valves, it might be somewhat from the inner tube, but I think most of it comes from the pump. In either case, I don't worry about it, as it's not important to be exact.

The question ended yielding lots of good answers, so once we changed the question to how to determine ideal pressure (rather than correct pressure), we brought up a lot of useful information.