From The New York Times,
"The grid certified by the city’s street commissioners on March 22, 1811, spurred development by establishing seven miles of regular, predictable street access. It also laid the groundwork for nearly 2,000 acres of landfill that would be added to the island over the next two centuries. The commissioners concluded that New York “is to be composed principally of the habitations of men, and that straight-sided and right-angled houses are the most cheap to build and the most convenient to live in.”
The grid, which incorporated some existing roads, would also prove surprisingly resilient. It accommodated motor vehicles (after sidewalks and stoops were pruned). It allowed planners to superimpose Central Park in the 19th century and superblocks like those of Stuyvesant Town and Lincoln Center in the 20th. In the 21st, the grid was extended west to include apartment houses on Riverside Boulevard."
Again--you might consider this a "duh moment"--the grid concept was very ancient, perhaps dating to the very first cities. "The urban grid goes back beyond Hippodamus of Miletus, the Greek urban planner, who, like the street commissioners, viewed the matrix as a manifestation of “the rationality of civilized life.” New York’s grid inspired planners elsewhere. But nowhere, wrote Edward K. Spann, an urban historian, “was the triumph of the grid as decisive as in America’s greatest city.”" Manhattan's long shape and reasonably flat landscape also suggested this layout.
One is struck, walking around Manhattan at just how few times the simple structure of the grid is violated--usually for a very good reason- a large public building like The Central Library; Grand Central Station; the old Penn Station or parks. Even in these cases, almost all these buildings or parks are easily traversed by footpaths.
The grid places the resident's ability to navigate and interact above the needs of the occasional visitor--who can always use public transit. This has limited Manhattan as a location for certain very large research facilities and has restrained the fantasies of architects, but it has provided widest degree of social interaction and the highest degree of convenience to New Yorkers.