Hi jlvelasco
Your assumption is not entirely correct; please kindly note that prices indicated by default are “from prices” where the lowest fare is usually the Supersaver ticket. If you select a train connection you will see that there are different ticket types. Fares for Supersaver tickets change according availability & demand and this is why you think the prices for the tickets are flexible. Supersaver tickets are only valid for a particular connection/train. I do not suggest buying a Supersaver ticket when arriving by air. In case your flight is late the ticket is no longer valid.
Prices for point-to-point tickets at standard fare, however, never change. They are set once per year (in December) and remain the same throughout the year. Look at such point-to-point ticket. It is valid for any connection for the chosen day and until 5 AM the next day.
Best regards,
Roland