In general, vocabulary correlates strongly with verbal intelligence, which is why it is on all of the gold standard individually-administered cognitive assessments. In my experience, the exception would be individuals with reading disabilities who have not had consistent, rich access to audiotext, who, often, perform much better on verbal reasoning tasks than on oral vocabulary tasks.
I would agree that those with strong verbal reasoning are also more likely to be able to deduce the meaning of an unknown word, in addition to having a larger vocabulary. Actually, that is likely a contributing factor to the preexisting larger vocabulary.
I also took the pre-1994 SAT, with, if I recall correctly, about 300 points of growth on the Verbal section over four annual administrations. That timeframe also corresponds with reading an average of about one novel per day, purely for pleasure (a bit under one for the first one or two years, and closer to two for the latter two years; I remember checking out a book from the school library first thing in the morning, reading through all of my classes, returning it in the afternoon, and checking out a book to read at home, which I then exchanged for a new book the next morning). I suspect it is not coincidence that my score rose 100 points between the last two administrations, when I was routinely reading about two novels per day on top of high school literature classes.
I would also agree that high school offerings can be quite different. At my private religious high school, my tiny class cohort of 40 had access to four years of Spanish, French, and German --but my calculus class was cancelled due to low enrollment (apparently one student was not enough to justify running the class!).
Another difference in reading expectations is in the shift away from literary toward informational text. At one point, college prep courses were focused on what we often call the classics, in preparation for post-secondary liberal arts education. With the movement toward school-to-work, up to half of high school English education has been shifted toward reading, comprehending, and responding to informational text, which necessarily has less complex vocabulary (there is certainly some very high level vocabulary in informational text, but as most of it is field-specific, it is more challenging to incorporate that type of text into a course for the general population). Differentiated classrooms also mean that many more students are hearing their reading selections read aloud, or on audiotexts, not because the majority of them would have been incapable of working their way through the written text, but in order to provide access to the minority who otherwise would be excluded from comprehension and response to text. This is a positive development for those with limited access to text (dyslexic, visually-impaired, some limited English proficient, etc.), but has the secondary effect of reducing the time-on-reading of all of the typical readers.
