Cookbooks have tended to be long lists of recipes. They're essentially lists of formulas and procedures, loosely organized by category: appetizers, fish, meat, poultry, vegetables, desserts.
Why don't we have more systematic cookbooks? Why not organize a cookbook by cooking method? Grill, saute, bake, braise, poach. Once you have an idea of what you're doing on your grill, for example, you'll do better at grilling everything. (It's really important, for example, to understand the difference between grilling, where high heat is everything, and barbecue, which needs a low fire and plenty of time.)
The success of Cook's is one sign of the interest in systematic cookbooks. Another is EGullet's successful "Culinary Institute" forum -- long discussion forum threads that explore one style or technique in great depth. A braising lab, for example, encouraged the participants to work together through a curriculum of braising projects, exploring techniques and alternatives while keeping other factore fixed.