cooking chemistry question

[boxofdelights]

So my daughter and I were making zucchini bread (delicious!) in my new silicone loaf pans (I love living in the 21st century!) and I said, "You mix the dry ingredients and I'll do the wet." And then I said, "The sugar was supposed to be a wet ingredient, actually."

And then I wondered why that is. Because the sugar would clog your sifter if you were using one? Because the sugar mixes better if it gets to dissolve? Those are just rationalizations, aren't they? Do you know the real reason?