I don't think that is actually true, particularly when you consider the cost of a train.
In comparison to tungsten and even fluorescent, the cost of drivers and the control equipment is much higher if you want to start dimming them. With tungsten you can just use a big resistor if you fancy it, where as LEDs require a whole pile of control gear, especially if you want flicker-free behaviour. This is why while you're likely to see some dimmable fixtures on trains, it's unlikely they'll have full colour and dimming control, as the demand for those features (on trains) is pretty much non-existent. On aircraft, where a significant amount of operating time is done with the lights dimmed and where there are actual safety concerns about adapting people's vision to night-time conditions, dimming and colour temperature becomes a bonus and the cost accepted.
Of course, what you lose in initial cost you gain in lifespan, with LED based sources being able to outlast tungsten and even flurry lamps by a significant amount - although there are plenty of LED products out there which tend to overdrive the actual emitters - reducing cost but dramatically shortening the lifespan (same ideas as under-driving the tungsten lamps discussed earlier to have a longer life). Unfortunately a lot of the early white LED sources were overdriven, and had poor phosphor design to boot (most white LEDs are a yellow LED with a blue phosphor) meaning they break early and go a horrible sickly yellow as they age.
Basically, if you want a long life, fully controllable LED light source, with good colour rendering and low maintenance, it will be significantly more expensive than just sticking a 100W old-school tungsten lamp on a dimmer.