For instance, you remark
> But that aeration pump they say you need on page 315, how are you to know who makes one that will last, and is supported well?
And to that I would say that first of all there are general strategies that can be applied to answering questions like this (systematically breaking down the problem). Second, with a very small amount of training in how to research and learn things it's often possible to track down that indirection. To pick on your specific example, I bet you that there is a textbook out there that college civil engineering majors use in their class when they study public works and it probably has a chapter on pumps that would at least help you figure out the specs necessary.
There is also an argument that by omitting facts that can change based on location and time (companies go out of business) the information becomes more timeless and easily propagated.
But like I said I agree with you in general. I think part of the problem is that the scope of human knowledge is becoming ever more complex and high level. In general people seem to accept that "getting the scoop from the grizzled veterans" is a necessary part of the process.