Adding "amtrak" to the domain name would require a license agreement from Amtrak, which is just a lot of unnecessary paperwork to deal with. I don't really have an intention of adding non-Amtrak timetables to the site -- the domain "timetables.org" is short and memorable, which is why I took it several years ago.
Well, just an idea for the future. Having other roads passenger timetables would be a very cool addition. Having people submit timetables would save some time for you two.