We're always open to criticism and suggestions. I sort of get where your coming from, but I'm not quite sure what you mean "rather than us having to always open a completed part to finish"? Certainly later chapters like the web services, and e-commerces one involve creation of the whole mechanisms from scratch by yourself.
Part of the problem is that in earlier chapters, we want to demonstrate simple concepts that require code and greater complexity than perhaps we wish to show at that stage of the book. So it's therefore easier to open code and amend it, rather than write it from scratch yourself. However I agree the step-by-step style is far more intuitive and I hope that if you perservere you find it more steadily swings into this camp as the book continues. We tried hard to get a balance that we felt was right, but we're always happy to make amendments and tune things we didn't quite get right first time around.