Am I missing anything? May be there is a way to create true distributed key?
There are N of M signing rules. Anyone can create the a transaction spending the coin. It is only valid if at least N of the M owners sign it.
This has to happen off chain, so as you say, it would require special software. The final transaction signed by N owners is then submitted to the chain.
As for a distributed key, it is possible to take a key (or any number) and split it into a "shared secret". This works the same way, if you only have (N-1) of the required shares, then you have zero information about the secret. However, once you have N shares, you can easily compute the key.