Like I've said many times before, if these games are coming to Europe, then they're guaranteed to come to North America as well. Xenoblade and The Last Story were both big budget RPG that Nintendo spent good money on making, and have a huge amount of content that will make any localizations pretty expensive as well. North America is Nintendo's largest territory, where most of their games get the largest sales. For Xenoblade and The Last Story, NCL isn't going to spend the kind of money they did to get both games made, and then spend even more to get both games an English dub, only to not release either of them in their largest territory.
This isn't like Disaster and Another Code where the games were both low budget titles that NOA and NOE were given the choice if they wanted to localize each one because they didn't cost NCL hardly anything to make. Xenoblade and The Last Story both basically rival Nintendo's top series like Mario and Zelda in terms of budget and as a result, Iwata is going to want the most sales he can get out of each one. This is why in this situation, NOA has to release both games because they have no other choice.