For transport you're right. I think the parent your referring to was specifically saying there's no alternative way to power a plane. That's my assumption at least.

if people prefer flying even if alternatives exist, like what's going on in Europe and Asia, then the alternatives aren't good enough -- price, convenience, availability, comfort, whatever reasons.

Even if some high speed rail existed in the US, do you think it is practical to go from California to Maine? If you are going 2,500 miles on a train that is going 150 miles an hour it would take you 16 hours assuming there are no stops. Obviously there are going to be stops so your trip is going to be an entire day.

I think a lot of people do not understand just how massive the US is.

For short trips. Most plane trips are at a distance where there isn't a viable alternative. Sure there are some nice trains that can handle the more common trips, but airplanes really shine for much longer trips.

Depends on where you're flying to and from in Asia, and how far.