I agree with you, that's a a way of binance to charge more fees.
It's okay to charge more fees, but it is not okay to make them hidden fees.
There is nothing written on the site about that, and they didn't specify it anywhere, I think that if they decide to do something like that, they should add it to the fee section, so people who uses the site will be able to know.

Not only that, if you buy XRP or something like that, you will probably find yourself staying with 0.8-0.9 XRP after you resold the coins, and you wouldn't be able to convert it into bitcoin or to withdraw it.