Look, it's a number!
Now, back in 1928, Pennsylvania Station was also serving through and commuters and Grand Central Terminal was serving through and commuters. These days, Penn is for Amtrak, and Grand Central Terminal is Metro North. But let's compare these apples and oranges anyway, via wikipedia entry for GCT, in the statistics section: "Commuters About 125,000 a day Visitors over 500,000 a day."
Other interesting observations from the entry: wow, there was an earlier 9/11. Who knew? Ok, probably everyone but me. For some reason, I thought it was interesting that that train station bombing occurred in the year between the two years that Moluccans hijacked trains in the Netherlands. In clicking around wikipedia, I also noted that Amtrak ridership and revenue has increased for six years in a row now. The route breakdown on where the big increases are happening also clarifies why Steiner is expecting great things of rail in the Midwest: it's one of those easy predictions, in that it is already happening, so you can be confident of your correctness.