Don't forget, cross-country air travel generally requires at least an additional 3 hours of travelling outside the city to and from the airport, checkin, security, taxiing, unloading, etc.
A five hour cross country flight really takes 8 hours, so a 15 hour train between city centers doesn't sound so bad. At half the distance, a 7 hour train vs a 5.5 hour plane excursion, sounds delightful.
This is true, but also applies to high speed rail. There are tremendous space requirements applicable to HSR that don't apply to regular rail. Look at HSR developments in China, Taiwan, etc, most of which have stations located well outside densely populated areas (except at points of extreme political/economic importance). Getting to a HSR station will be non-trivial also, not unlike getting to an airport today. HSR directly into a place like Midtown Manhattan is unlikely.
A five hour cross country flight really takes 8 hours, so a 15 hour train between city centers doesn't sound so bad. At half the distance, a 7 hour train vs a 5.5 hour plane excursion, sounds delightful.