I roamed the aisles of adult fiction at the library and then at Barnes and Noble, randomly selecting titles of classical and modern writers whose success has made them household names. I did give attention to publication dates in order to have a decent representation of novels throughout the decades.
With the emergence of genre fiction, maybe writing has become more commercialized. Or perhaps the shift is due to the fact that writers are forced to pull in agents and editors (as well as potential readers) with a first sentence that cuts directly to the point. No more time for elaborate sentences and elegant words that can paint all sorts of meaning.
Look at the dates. Read the first lines. Compare how your first line measures up. See if you notice the shift.