Railteam, the alliance of European high-speed rail operators, has shelved plans for a Europe-wide common booking system because of increasing costs.
Continued at: http://news.bbc.co.uk/1/hi/business/8382508.stm
I think we agree that is a disgrace, however it is the case that complexity of fares at present make finding the cheapest route infeasible. Given the fact that one often needs add up different fares, the principle complicating fact is the existence of return fares means that outward and return journeys must be considered together, rather than separately, which squares the number of steps needed. Also the interaction between different fare systems adds complexity.
Of course the fares should be simplified to solve that problem, another potential cost is making ticket printers compatible with other train operators ticket gates, but ticket gates are rare on long distance services outside the UK.