Well, the word of mouth for Xenoblade was ridiculously good based on impressions of the Japanese version. And lots of people who would be interested in a high quality, vast and epic RPG probably did own Wiis. Maybe not as their primary platform, but for someone disappointed at what happened with FF13 and other console RPGs this gen, they'd eat up XB.
Nintendo really screwed the pooch in a lot of ways by refusing to localize Xenoblade. I think that the whole Operation Rainfall debacle, which happened during a time of Nintendo alienating their hardcore base (while continuously chasing after the casual market), is what really damaged their perception coming into the WiiU.
Sometimes, companies need to 'bite the bullet' and take the risk... cater to their hardcore fan. Since those people will be the ones who will stick with you through thick and thin, they will be the ones talking up your system/your game to the lesser informed. Seems they're learning this lesson with the Wii U, but that's a bit too late.