The main dichotomy in political geography you have in the US is the opposite sides of the Mississippi River. You do have a transitional zone in Illinois (which nowadays as migrated to Chicago), but to a coarse approximation, even the rail magnates of the Gilded Age are unable to build systems that truly cross the transitional zone. In the West, the big prize is connecting the ports on the West Coast with ultimately Chicago, with lesser prizes for feeder lines to bring the products to Chicago. One of the big purposes of the land grants, after all, is to encourage settlement of agricultural lands in the area.
But in the East, the prizes are connecting to the Northeast ports (or Chicago, or to a lesser degree, the other major cities in the Mississippi River). And most of these lines aren't affected by the existence of the Western US. The commercial center, say, an Ohioan is looking towards isn't San Francisco, it's New York City. Rip out the land grant system, and you wouldn't reduce the viability of all of the lines being added in Ohio; although the lines people are working in, say, Indian Territory, will suffer mightily. But the latter are already in the not-dense portion of the network, whereas the former are in the dense part of the network.
It's really not until the mid-20th century that the Pacific Coast takes on the commercial significance that it has nowadays, by which time the railroad trackage of the US is beginning to decline as consolidation takes place.