Because you have to log in and out each time you use it. It's no different than using one of their computers.
Now, if you are just using Word and not logging in, then there's no charge. A lot of people will write their report or e-mail or whatever in Word and then log in and send it through their e-mail.
Let me tell you, the internet is often very slow depending where the ship is, so don't expect it to be as fast as you have at home if you are on high speed. It's more like, low, low speed.
Everything you pay for on
the ship is in US$'s. The charge for using the internet will go on your bill.