The process is not the same just like boiling is not the same as frying. You preheat the oil before you put the egg (or whatever) in it. The high temperature fries the egg. If you put the egg in cold oil and then heat it, you end up with an egg boiled in oil as it does not reach the same temperature.
Pretty much the same thing in an oven. 20 minutes at X degrees is not the same as 30 minutes at Y (lower than X) degrees. You end up with a different product. The most obvious thing is the crust which forms first due to the high temperature. In a non-preheated oven it would not form initially. Same thing with microwaves. The process is just not the same. You cannot bake bread in a microwave and get a crust because the very high heat outside which forms the crust is not there.
[hijack]One of the things I dislike about homemade bread is the thick, crisp crust. I can only eat the soft center, the crust hurts my mouth too much. How should I alter baking to get a softer crust?
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Try using milk instead of water, and be sure the bread has a small amount (usually 2-3 tablespoons max) of butter or oil. You can substitute granulated soy lecithin one-for-one; it’s completely natural and available in health food stores or from the Baker’s Catalogue (www.kingarthurflour.com).
Another possibility is a “pain de mie” or “pullman” pan, which is a bread pan with a lid. They’re pretty expensive, but you can substitute putting a cookie sheet with a weight on it over your bread pan. I haven’t tried this myself yet; I’ve been wanting to. A number of my baking books recommend it for a fine-grained, soft-crusted bread. IIRC you need to adjust your recipe for this method, so you might want to scout around on-line.