You seem to be mixing up a double boiler and a pressure cooker. The articles you read are correct - the temperature in the double boiler is lower when the inner vessel does not touch the water.
First, in a double boiler, the steam-air-mixture will not get above 100 C. Instead, the steam will expand. This is why you see a cloud of vapor rising out of the double boiler. And new, cold air comes in, so you don't even have a 100 C steam, but a below-100 mixture of air and steam.
Second, the food does not touch the steam. It touches the inner vessel. On the outside, the steam touches the inner vessel. But it is not simple conduction of heat that happens on the boundary; the steam also condenses on the surface of the inner vessel, which uses up a lot of energy, and reduces the temperature of the inner vessel. (This is also why steaming is a slower cooking method than boiling).
Third, I am not entirely sure what the temperature equilibrium of a double boiler would be - whether it is very close to 100 C, or noticeably below it - but you usually don't cook in a double boiler at equilibrium. It heats up slowly (see the above two points on heat transfer) and that time allows you to heat your food very gradually. If you were to hang the inner vessel directly into the water, it would soon come up to 100 C (especially the thin steel vessels that are frequently used for double boilers) and then the bottom of your food would be prone to overcooking. In such a case, you can just about save eggs, if you stir or whisk them with sufficient intensity, but any chocolate will distemper badly.
So, in summary, if you want your food to get heated slowly, don't let your double boiler's inner vessel touch the water.