Banks that skim money from wires

I'm finding that wire transfers in Europe are not necessarily free. The bank might say they are, but when money goes to or from a forex account, intermediary banks are taking some of the money as it goes through.

For example, say someone sets up an xtb.com forex account. xtb.com claims on their website that there is no fees for funding or withdrawals. However, the bank they use (Pekao S.A Bank) simply takes some undisclosed amount of money as it goes through.

Another example. You send money to your varengold.de account, which is supposed to have a free wire transfer in amounts over 12,500 euros. Their bank (Dresdner) skims some of the money on the way through.

Is this legal?