No problem.
While I'm not cruse ship expert, here's what I suspect. The tides certainly affect them as well, but it doesn't play as big of a role because of the extreme length of the lines. When the tidal change is 3-4 feet, and the lines are tied onto the boat 50 feet from the pier, the tidal change has a relatively smaller affect on the line tension. In addition, I suspect the difference can just be stretched out of those lines because of their length (although I don't know if that's what they do).
It would be important to keep the ship carefully in place relative to normal boats largely because of the importance of it sitting still. Think of the passengers coming on and off, and cranes (or whatever) loading and unloading cargo, etc. If a slight breeze were to come along and it wasn't tied tight, someone or something could get hurt/damaged... There's also a lot more momentum that can be created when those suckers move around and could cause more damage.
This is what I suspect. In addition, because of the man power on these ships, perhaps they adjust the lines frequently enough to keep them tight, but not too tight (not forcing them to stretch).