Most places are charging $40 or more for physical copies, even higher for a sealed copy. So the eShop version is more than 50% cheaper than you'll pay for a physical copy.
Not true at all
*snip*
Some places are trying to sell the game for $40 or higher - but (as links posted above clearly show) finding it for less than the eShop asking price isn't difficult. Plus, if you own an actual copy then you can choose to sell later and recoup some of the cost - especially useful for people who find out they don't like the motion controls in this game, since motion controls are a huge part of the game.
Speaking of which, I liked the motion controls. Most of the time they were fun and relevant, but Phil is right about one or two specific points at the very end of the game being very poor. The sword fighting motion in particular comes to mind. Controls were still manageable though - and probably less annoying overall than the sudden death trial-and-error moments found in the game.
Lots of griping in that last paragraph, but Zack and Wiki was still a great experience on Wii and comes highly recommended.