Of course, as the thread is built on the wonder of generalization, I will continue with generalizations myself.
I truly believe that many, if not a majority of highly intelligent people (however one wishes to define intelligence), are stuck in lowly jobs and for a variety of reasons.
First, I think intelligent persons are prone to contemplate life and the world, at a more frequent and deeper level than the average person. With this contemplation, I assume or infer (another generalization) said intelligent person realizes the horror or folly of much of society, and also of their own meaning in relation to it. With this full knowledge, a great many of these intelligent persons decide to rebel against the world. This rebellion includes finding lowly jobs that have no relation, nor help to support or further the present day society: pointless bureacratic jobs, lowly coffee house jobs, etc. Other very intelligent persons, rebel by a total lack of ambition in their current job; happy to be stuck in a moderately paid position with little influence or power, as the very assumption of power in something the intelligent person considers corrupt or pointless, is a form of acceptance of the corruption, or of the actual meaning of the job. I truly meet countless very intelligent persons who fulfill one or the other category.
Second, and building upon the previous paragraph's reasoning, this contempltion also relates to other aspects of life, such as operating in society, building a family, etc. As contemplation of the world/society and ones meaning in it, reveals the pain, folly, meaninglessness, and corruption of it all, many said intelligent persons decide not to reproduce, or to even to marry. Many others refuse to take part in the usual everyday acitivities of society--entertainment, parties, television, pop music, movies, etc. as they find them pointless and meaningless.
Sure there are many intelligent persons who do go on and become integral parts of society--furthering it, sustaining it, being a part of it. However, I have noticed that many successful businessmen, developers, capitalists, bureaucrats, (insert job here), are those of average to above average intelligence, who do not contemplate the world or themselves, and thus go forward with enthusiasm, ambition and vigor with their lives (be it work, family, etc). So, yes, based on experience I have noticed the thread starters comment to be true.