As we all know, writing in all caps equals to screaming or yelling. Now, imagine a ship in a storm, with wind howling in the masts and waves crashing on the deck. In such situation, would you gently whisper the name of your ship to your fellow crewman's ear?
Last time I saw a ship, the port of registry was also painted in all caps. I checked DNV Exchange and even there it was in all caps. Still, that vessel was registered in Helsinki and not in HELSINKI...
Many documents use all caps for ship names because not too long ago that was the only way to emphasize text. However, for example Wikipedia uses italics instead, a style which I have adopted for professional work as well. For ShipSpotting.com, I'm willing to accept all caps because the name next to the photograph is more akin to a database entry than a word in a text, but God forbid any of you from using it in forum posts...