The issue is not poor grammar or completeness of information. The issue is clarity. You’ll agree that the use of punctuation is a part of good grammar. However if we look at a sentence from the example passage, punctuation is hardly in evidence:
The increase in the numbers of married women employed outside the home in the twentieth century had less to do with the mechanization of housework and an increase in leisure time for these women than it did with their own economic necessity and with high marriage rates that shrank the available pool of single women workers, previously, in many cases, the only women employers would hire.
As the author of the article says, would this sentence be of acceptable standard on the written portion of the GRE?
Besides, the mark of a real test is that if all the elements of good writing were present and a candidate still got poor scores, only then could the candidate’s reading comprehension skills be considered truly poor.