Betty Crocker-free zone

I am greatly benefiting from being here, surrounded by the amazing cooks in our mission. They share all their recipes with me, and I can’t believe how simple it actually is to make most things. I've had my problems. For example, did you know that garlic salt and garlic powder are not the same thing? And that mapeline can not be substituted for vanilla? But overall, it's been "a piece of cake." Now, I’m not saying I’ll continue to roll out tortillas or strain curdled milk to press out my own cream cheese when I no longer need to. But to whip out a cake with hardly a second thought? Awesome!
I do have a question, though, for all you chemistry buffs out there. Take the following recipe for Wacky Cake (try it, it’s amazing!)
3 c flour 2 Tbsp vinegar
2 c sugar 2 tsp vanilla
½ c unsweetened cocoa 2/3 cup oil
1 tsp salt 2 cups cold water
1 ½ tsp baking soda

Mix first 5 ingredients together well. Make 3 wells in
the powder: in 1 well, pour vinegar, in the second,
pour vanilla, in the 3rd, pour the oil. Pour cold water
over all of it, and mix well. Bake at 375 for 35-40 minutes.

Ok, I’ve already admitted I’m still a novice, so I haven’t ‘rocked the boat’ enough to try making this cake without following the directions. But will someone please tell me: why the wells? Is there some chemical reason the three need to be separated until it’s all flooded with cold water and mixed together? It was never covered in my General Chemistry class, I’m afraid, and it’s driving me crazy!
(Jon Rhoad, this one’s for you)