As some of you may know, I'm a mathematician, and I have to say that there can be space on a particular topic for a mix of high and low level content. Taking, for example http://en.wikipedia.org/wiki/Julia_Sets
, the Wikipedia Article on Julia Sets, we see a fairly readable intro which admittedly uses the words "complex dynamics" and "holomorphic function." Now, the average reader who doesn't know what these are will skip over these, perhaps picking up on "complex" and "function," depending on how advanced a mathematician they are. However it goes on to say that "informally consists of those points whose long-time behavior under repeated iteration of f can change drastically under arbitrarily small perturbations" and that the behaviour of the function on J(f) is "chaotic." Now, for the user who is reading this with some vague interest, this description should be reasonable. Wikipedia cannot be aimed at people with absolutely no knowledge in the area - how would this article be written? "A Julia Set is a kind of Fractal which is made from some Function..." and then we kind of peter out of ideas for the layman?
One of the articles that the article itself points out as a bit rubbish on the layman readability front is http://en.wikipedia.org/wiki/Mitochondrion
. As a mathematician, I've always had an issue with Biology, but I can still pick out some phrases which give me reasonable information to what a Mitochondria is: "In cell biology, a mitochondrion" tells me it's a part of a cell, "Mitochondria are sometimes described as "cellular power plants," because they churn out energy for the cell", the cell structure part gives a nice image of a mitochondria, and the mitochondrial functions section gives me more information on the energy conversion and its other uses. I would say that this article is a good example of a Wikipedia article being readable to the layman (with a basic degree of Biology knowledge, otherwise why would they look at it) with enough information for the expert.
In conclusion, I don't agree with the original article's sentiment, and believe that Wikipedia Science articles are, in general, readable enough to laymen, and have enough information for experts.