I'm sure Capcom is definitely happy with the 300k for an adventure game with no advertisement. However I think the Japan+US retailers overestimated Zack & Wiki's sales since only like a third of the shipment was sold to gamers, which means if a sequel is released, the retailers would very likely order a much smaller shipment.
But even if that shipment was on par with costumer sales, Europe would still be Z&W's saving grace, the region that accounts for most sales of adventure games.