You know, that's funny. When my wife and I got married many years ago, I noticed that she'd basically turn on the oven and throw whatever in to cook. I'd be like, "what are you doing? You know you've gotta let that thing preheat first. Otherwise your timing as far as when the food is cooked is going to be off!" I was very much a recipe follower to the T. Of course I lived on my own for several years before marriage and used my oven for off-season clothes storage, and I couldn't even tell you if I had a gas or electric stove!
Well, what the hell do I know? I've migrated to that same behavior over the years. And you're right: unless one is baking (where exact science is important), it really doesn't matter. Your food will get cooked, and as long as you know what you're looking for (how to check for doneness, etc.) you can manage it.