Shannon and Weaver's model purports to offer a neutral, objective way of talking about communication. But as the figure suggests, the model relies on a particular worldview, a scientific and mechanical version of communiation and meaning. Not surprisingly, many people in composition (and almost every field) have developed much more complex, socially situated models of the communication process that take into account the reader's role in the construction of meaning, the contingency of meaning, the context in which communication takes place, politics, and other factors. Shannon and Weaver in fact later complicated their own model by introducing channels for feedback; more recent approaches have in turn provided more dynamic approaches, but the overall approach is still remarkably the same.
Why, then, are we still able to position ourselves so easily in this simplisitic model when we use online documentation? Simply because it works. Just as Einsteinian physics replaces Newton's laws, people still apply Newtonian physics in their everyday experiences in the world. So what if the old model is slightly off? It works well enough for most purposes. The key phrase is "works well enough": by defining the success of the project in terms such as speed and accuracy, such texts map out other concerns, from broader conceptual knowledge to the politics of technology.
So whereas early forms
of online help attempted to naturalize themselves by appearing as books on screen,
complete with spiral binders, index tabs, and a three-D look, designers and
users have quickly discovered that what hypertext offers was not a way to improve
on an old, slow-moving technology, but a way to create a new machine, one we
occupy in order to navigate information space. (It's so fast it doesn't move.)
We are told by this machine that the Shannon and Weaver model works after all,
once we have attained a level of technology poweful enough to support the (mainly
one-way) process of communication. In print, the medium was the message, but
that was always the problem with print-it got in the way. Online, we can make
the medium disappear and leave the pure message.
The emphasis here on transparency in technical communication is not a surprising
or even recent development. Technical communication has long been framed by
its practitioners as an activity and discipline in which the medium should (ideally)
be transparent: 
Robert
Connors' (1982) history of technical communication identifies the splitting
off of technical communication from English departments as due in part to the
heightened sense of a need for efficiency in functional and technical prose
(p. 332). And David Dobrin (1983), while maintaining a critical stance on both
the fluidity and power of definitions, notes that "technical writing's
greatest success comes when it is swallowed easily and digested quickly"
(p. 247).
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