The funny thing about stock value is that it's not really a proper indication of company value. Stock can change overnight, while the actual money involved in the company (everything on the balance sheet) hardly changes.
This is not to say that Nintendo isn't doing great, but be realistic.. I think the stockvalue of Nintendo is overrated on the surge of success the company has had. Deserved success sure, but make no mistake, Nintendo is not anywhere near the size of a company like Sony.
And before anyone says so: no, this does not mean Sony/MS are doing better than them at sellin consoles or even have better profits. All I'm trying to say is that stock value is a very relative (even fickle :P) thing and not neccesarily the best way to measure the worth of a company.