Not quite sure why you wouldn't want to preorder Xenoblade Chronicles, but Nintendo has commented on the rumor that the title will only be available to those that plop down some cash prior to release.
Thanks for contacting us. I can confirm the Xenoblade Chronicles will be available exclusively for purchase through U.S. Gamestop retail locations, www.gamestop.com, and www.nintendo.com.
However, Nintendo never stated that it will only be available to those who preorder it. Also, the website that you mentioned in your email never stated this either. Preordering simply increases your chance of acquiring a copy of the game at or near launch time.
This means you should be able to walk into GameStop on launch day and grab a copy, preorder or not. Thanks to Autosaver for the heads up!