Nintendo (in the past) tried to compete on the same values as other companies and, even though they were quite successful at satisfying those values, had significant problems in maintaining their market share. By focusing on different values than their competition they created an asymmetric market which ensured that they could grow their market share by facing little direct competition.
Part of the reason Nintendo (seems to) focus on surprising their customers is to ensure that their product will remain distinct in the market. If Nintendo announced the features of the 3DS a year earlier, by the time Sony announced the NGP they would have already copied most of Nintendo’s unique features and weakened Nintendo’s strategy; and if Nintendo continued with a carbon copy of the Wii strategy, or announced their next generation system a year ago, Sony and Microsoft would have time to create a response to their product before Nintendo even released it.
