For every train, there is a fixed number of tickets per price category. So sometimes, you can still find cheap tickets ("super sparpreis") a day before because thag specific train didn't have many bookings:)
Aw hell they picked up on that stupid American capitalist crap?
I worked in Germany in 2005 and back then everything was fixed price per kilometer for each train class, and you could get rail passes of sorts and get on whatever the hell trains you want during their validity. I'd take train roundtrips after work just to watch sunsets.
The price concept discussed above applies to long-distance trains. Local trains are still different, especially if you have the "Deutschlandticket" (germany ticket) you can just hop on any local train you like.