Putting aside the aerated types, such as Wonder, the difference is that European breads tend to be firmer and more chewy, whereas Americans prefer a light, airy crumb. Even back in the day James Beard noted this difference, and provided an American style bread that used milk instead of water, and added a little butter.
Contributing to the difference is the flour used, the yeast, even the water. And the methodsused to combine them. In other words, there's no simple answer. Even in France there are vast differences, one bakery to another, and people have actually come to blows over who makes the best baguette.
We are, of course, talking about white breads. The fact is, there is a long line of European breads that do use amendments and enrichments, especially for, but not limited to, celebrations and holidays.
It should be noted that, with the growing artisan baking movement, more and more Americans are making European type breads at home. And the number of artisan bakeries seemingly grows on a daily basis. Whether this reflects a fundemental change or merely a fad depondent sayeth not.
Aside: Siduri, you got sumpin agin water? Bread is made from four ingredients, not three, and, where the law runs, all four are specified. When you think of it, there's a fifth: magic; the alchemy that coverts those four humble ingredients into the wonder of bread.
Also, what your ideal way to make a dark, crusty, porous bread in loaves for dipping in olive oil and herbs or making sandwiches?
TKChef, you're asking an awful lot from one loaf. Those are different requirements, and you need different approaches and forumula to achieve them. For instance, a good dipping bread is open and porous, with random sized holes. A baguette typifies that construction. On the other hand, for sandwiches you want a tighter crumb, with smaller, consistenly sized holes.