I'm definitely in the camp where you don't need to be an expert in a field to be able to invest, though I'm sure there are specific companies where it is "too hard" unless you are such an expert. With the caveat that I have not read these particular primers yet, but thought they might be a good resource, there is a large difference between a primer and over-reading industry information. In my mind, a primer is useful for giving you the conceptual models for operation of companies in the industry and letting you understand the esoteric language that is used. For example, if you don't understand how reserving works in insurance or banks, or the language used by companies in that industry, a primer in reserving may be the means for helping you understand the SEC filings. The cost of 100 or 200 pages of reading to be able to more fully understand a 10-k is not that high, particularly if it helps you understand each further 10-k in the industry for the rest of your life.
Moreover, there are times when you want more information about the industry or a company after reading the 10-k to round out your knowledge. IMO, there is a fine line between over-cluttering your mind with information and the Dunning Kruger effect (http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect).