For whatever reason (probably just inertia), JR has been highly resistant to adopt dynamic pricing, so Shinkansen tickets costs the same regardless of whether you travel at absolute peak or when the trains are rattlingly empty. This is starting to crumble at the edges a little bit, and I expect advance-purchase fares to plunge if they ever do make the leap.
Yes it's one of the reason to choose airplane for individuals. Govt's regulation for train is an another reason why dynamic pricing aren't done well but it's changing. Currently train+hotel Dynamic Package is available as a cheaper option, but it's not for single day use.
Oh, neat, I recall a trial of that but didn't realize it was rolled out permanently. And apparently you can even book tickets online without jumping through insane hoops! Huzzah!
