They all use the bank zachodni because german banks close bank accounts if you trade with the wrong bitcoin user. It happened to many and im glad i read about it before risking my account. It would mean a lot of work and trouble.
They do this because they fear connection to money laundering. In order to not have work they close the account. There are enough other users that dont mean a risk or work.
Heres a thread about it. Unfortunately in german: https://bitcointalk.org/index.php?topic=98434.0