It makes PERFECT sense when you think about it.
Railfans spend absolutely obscene amounts of money on their hobby. Yeah they get something that is really cool and that they made out of it, but still, it's like Warhammer on crack ^ 3.
So someone comes along and says "Hey, here's a game for sixty bucks, you can actually drive around in first person!" And they say "Now that's cool...but uh, I could just put a camera on my train!" And then they say "But could you drive it a few hundred miles along the coast of the United Kingdom?" And they go "Ooooooh."
Later on, you come back to them and say "How would you like a new locomotive for twenty bucks?", and they say "!!! If I bought a new REAL model engine like that, it would set me back five times as much!" And you say "How about a whole new terrain for thirty bucks?" And they say "Well that's pricey but if I built it myself my knees and my back would hate me forever!"
PERFECT. MARKET. They expect to pay a ton, and you can give it to them almost for free.
And at the end of the day...for people who don't play other video games, and think that these graphics are totally awesome, for whom the game is exactly the game they want, the PERFECT game they want, the Dwarf Fortress of Trains...how can you say it's not worth the money?