That's an exaggeration. Airlines will tell you to arrive at the airport 2 hours before your flight but if you're a bit organized, check in online, know what you can and can't pack in your carry-on, I'd say 90 minutes is fine. I usually end up sitting at the gate for about an hour waiting for boarding if I arrive 2 hours in advance.

Even so, a flight from Chicago to San Francisco is a little over 4 hours in the air. A train takes 2 days. There is no comparison.