You could say as much for beanie babies too. They will be limited so therefore valuable. Forget a hundred years from now that people might not see any value at all in a plush doll, or some runescape gp, or bitcoin. Meanwhile, something like iron or gold has held value for all of human history.
Bitcoin only makes one relevant promise: There will only be 21 million. And that means that the people who are born poor get a chance at building wealth by not having the government constantly reduce the value of their money. Bitcoin is an escape from the system that keeps people poor.