Vannevar streamlines Wikipedia reading by pulling linked content into the current article.
Complicated subjects build off an understanding of other complicated subjects; in order to understand a given Wikipedia article, readers often need to visit multiple pages. Skipping between several pages at once disrupts reading flow and increases the cognitive strain to keep track of the information paths being traversed. Vannevar pulls the first paragraph of linked content into the current article making for a more linear reading experience.
Because Vannevar exposes linked content by default, it doesn't need to be displayed manually. This approach is usually avoided in favor of progressive disclosure, but here, when we know the reader will return, it reduces disruptions. By arranging the text in a single column, the content maps well to scrolling. The interface demands less physically: the hand stays anchored to a fixed point and the eyes aren't diverted from the text. What scrolling lacks in precision, it makes up for with a cognitively easy "undo"—the same scroll action in reverse. While Vannevar will almost surely display more content than necessary, the new content is identifiable, which aids our ability to skip extraneous parts—a reading practice we're rather good at anyhow.
A good analogy might be public transportation. We're usually willing to take a slightly longer route in order to avoid multiple transfers. This choice may require travel out of the way past a few irrelevant (to us) places, but the tradeoff is worth it. Absent the stop-and-go of switching subway lines, we can sink into a book, a crossword, or a nap with fewer interruptions.