Be very careful in how studies of causality are performed. For one
thing, you cannot determine success factors if you only look at
successes. You must do an equal analysis of failures. Of course, it is
difficult to get the information on failures, but if you do, I think
you will discover that many of the failed products have precisely the
same attributes as successful products, both in the product and in
company structure and processes.  That will severely impact your
conclusions.

Note that in science, positive instances that confirm a hypothesis are
considered weak evidence. The strongest evidence e is that which can
possibly disprove the hypothesis.  A standard question asked of many
people's hypotheses is "what kind of evidence would show it to be
false?"

AS for Apple, I was a Vice president at Apple between 1993 and 1998,
which includes the survey period you reference covers.  I have reads
many cade studies of Apple, and with one exception, I found them
incomplete and inaccurate. You have to remember that the way a company
looks like from the inside during some period is very different from
what the company looks like from the outside. Companies always look
far better from the outside.  The problem is far worse when the
analysis is done at some later date when the outcomes are known. In
psychology, this is called "Hindsight bias."

I have my own private reasons for the failures and successes of Apple.
A lot has to do with the people in charge and the culture around them.
I also distinguish between the two Steve Jobs, Jobs I and Jobs II.
Those were different people, Jobs II havening had a lot more
experience in several companies and who was far more mature than Jobs
I. Note NeXt computer, developed in the years between, was also a
commercial failure, even though the same product and people became
successful when they renamed NeXt into Apple.

I am NOT going to tell my story.

--
Anyway, please look at disconfirming evidence. Look at failed
products.  The Apple Cube is one example. So is Apple TV. So is Apple
III. The Macintosh was almost a failure -- it was saved by the
combination of Canon's inexpensive laser printer, Adobe's typesetting
software (postscript) and the availability of cheaper memory and the
first large hard drives (20 MBytes, so much storage space people
wondered how they could ever fill it).

There were a whole bunch of other failures. The Apple Digital Camera.
 The Lisa. The Apple CDi player.   In more modern times there are
others.

Moreover a lot of the failures never became products. Instead, a
product team would spend years, with sometimes hundreds of people,
only to be shut down at the end. And not necessarily for good reasons.

These stories are true of every single company and industry I have
examined.  Anyone who simply looks at the success stories will miss
what is truly important.

--

One thing is true, however. There is NEVER a success or failure caused
by a single factor. You may wish to look at design, but design,
usability, cost, market differentiation, marketplace acceptance,
corporate culture, advertising, positioning, customer acceptance, ....
  All play critical roles. No single one is responsible for success.

If you look for easy answers, you will find them.  But they will be wrong.
----

I said there is one case study I trust. It was done by Thomke, at MIT.
 He and I corresponded about it. Even so, this study is incomplete:
Thomke points out that Apple denied him access to the key players, so
he only had access to published accounts (and some interviews with
former Apple employees, such as me).   We recently discussed this
paper again and I re-read it carefully. I found nothing wrong, but the
story is much more complex, for reasons I will not talk about.

http://hbr.org/product/design-thinking-and-innovation-at-apple/an/609066-PDF-ENG
CASE (SECONDARY SOURCE)
Design Thinking and Innovation at Apple
by Stefan Thomke, Barbara Feinberg
Source: HBS Premier Case Collection
13 pages.  Publication date: Jan 09, 2009. Prod. #: 609066-PDF-ENG

Describes Apple's approach to innovation, management, and design
thinking. For several years, Apple has been ranked as the most
innovative company in the world, but how it has achieved such success
remains mysterious because of the company's obsession with secrecy.
This note considers the ingredients of Apple's success and its quest
to develop, in the words of CEO Steve Jobs, insanely great products.
Focuses on: 1) design thinking; 2) product development strategy and
execution; 3) CEO as chief innovator; and 4) bold business
experimentation.


=====

Good luck.

Don Norman