I thought that dehydrated produce only differs from fresh produce in containing less water, so why do sun-dried tomatoes taste so different from their fresh counterparts?
There are a number of reasons why the flavor of tomatoes changes during both the cooking and drying processes.
The first is that when drying the tomatoes, farmers and processors will dust the tomatoes in fairly high levels of salt, which helps to keep harmful microbes and insects from eating into the fruit and causing rot and infections.
The second is that when drying anything, you need to remove the water from the flesh of whatever it is you're drying. This causes all of the flavor molecules to become more concentrated. The resulting flavor is more intense because there is simply more flavor per bite.
The final and probably most important (and beautiful:) reason is chemistry. Tomatoes play house to something like 400 volatile aromatic compounds - that is, molecular structures that change and break apart during the acts of heating or drying. While I don't have the EXACT science in front of me right now (and can't seem to find it on the interblags) there's strong indications that it has quite a bit to do with the structure of sulfur-heavy amino acids, c6 volatiles, and glutamic acid breaking down over the course of the drying process - due to the evaporation of water and introduction of salt - and changing into different aroma molecules.
All of these, taken together together have a profound impact on the flavor profile of sundried tomatoes.
The flavor is usually more intense. If the tomatoes are picked at their perfect peak ripeness and put out to be sun dried, the flavor is indeed more intense. Also what can happen is that they are packed in olive oil that may have some herbs or seasonings like garlic or basil or just the oil, what kind of olive oil and where is it from may cause it to taste different. Fruits that are sundried are not usually packed in oil but just dried. They are usually more intense and it is because it is the fact that the flavor is more condensed and then more intense as long as you have good sweet fruit to start with. Also if you plant your own tomatoes you will notice a different taste as tomatoes bought at some markets are refridgerated, may be picked green so it turns red on its way to the market. Also many times plum tomatoes are sundried and not all varieties of tomatoes are sundried. Also the regions of where the tomatoes are picked, ie Italy, Spain, USA, anywhere in the world may cause the taste of the tomatoes to differ. My own grandmother used to do this at her home with fruits and tomatoes and made something like the "fruit roll-up" that kids eat, but it was more intense and thicker. She made apricot and strawberry (it was out of this world delicious) and it is a lost art today for home cooks today. People on farms seems to do this here and there but not many people in the city.