Wow, there is a lot of dissention going on in this thread. Some very good points are raised though too.
Let's not forget that Americans are not the only ones taking cruise vacations so the practice of tipping does not JUST involve American policies. Every country is unique in its service industry and I think everyone should respect their rituals so to speak when you travel.
I do believe hospitality workers are underpaid, but don't blame the whole industry based on a few that unappreciate your "gift" to them for their service. I too experienced this treatment on my last cruise after giving out the tips, but I am not bitter enough to not take another cruise.
Just have fun, and remember all those memories you received after traveling!