I would argue that HAL is still a Dutch company despite being American owned. Do they predominately cater to Americans? Yes of course they do but I don't think that should require them to dumb down their names for the American market (that is after all what we are talking about here). America as a country is absolutely littered with names that are difficult to pronounce and confusing to non natives of a given area. If we as tourist on the great American adventure can adapt to names like Chattahoochee, Monongahela, and Pascagoula certainly we can handle something like Oosterdam and Zuiderdam.
I don't think Adventure breaks the chain as much as you contend. Adventurer would have been better I grant you but it still keeps to the theme of exploration and discovering started with Voyager. The two newest ships are probably the worst of the lot IMO but they are still far better then a lot of the other lines IMO. I think it would be nice if they would go back to the Song theme that RCCL did in it's early years, with Song of America and Song of Norway. Even the public rooms where designed around the concept of music an musicals with names like the King and I dining room and the Guys and Dolls lounge. Additionally I always felt Nordic Prince, Nordic Empress and Sun Viking were equally classy and workable names. Of the Seas has become such an iconic part of their image at this point however I would imagine it is unlikely that they will move away from it. It is as much a part of RCCL's current image as the old IC and IA naming conventions of White Star and Cunard once were.
Honestly I'm far more concerned with the increasingly ugly box shaped ferries that so many of the shipyards are turning out today then I am with some of the naming concerns expressed here. That is something that RCCL at least tries to avoid as their ships still have a semblance of nautical design and beauty to them that is sorely lacking in the ships being produced by most of the other lines now.