The general fact that they passed Sony makes no sense. Sony makes way more products that Nintendo doesnt. Sony makes computers, TVs, CD Players, Movies, owns a music company, makes car audio, stereos, game consoles, and handhelds. Nintendo made board games (do they still do this?) then moved to consoles and handhelds. Nintendo's stock is nothing more then inflated stock that will crash down like the Chinese stock market eventually.
a) nobody is saying "general" fact. it's just one measure--but an important one.
b) you're looking at revenue. if revenue is all that matters, GM or Ford would be worth a lot more.
c) inflated stock price: that's your opinion. i've thought for years Google and Apple stock are way overvalued, and nothing has stopped them yet. and now they're both worth about 3 times as much as Sony. not saying Nintendo can keep growing forever, just saying that your guess, my guess, and everybody's guess "average out" to the current stock price, and nobody knows what the future hold.
the market cap is a non-intuitive measure. i remember many years ago when Microsoft first passed big blue, aka IBM in stock market capitalization, many people had similar discussions. they say, "it makes no sense", "Microsoft stock will fall", "IBM still have way bigger revenue, way more employees, they just need to turn it around". guess what, it stayed that way. and even today, IBM has double Microsoft's revenue and 4 times as many employees. Microsoft simple is more PROFITABLE. today, Google has a bigger market cap, i.e. "more valuable" than IBM--does that make any sense? hey, that's what market cap is. sometimes it's non-sensible, but to some, it's more than sensible, otherwise they wouldn't be valuing the company at that price. that's how equities work.
sony will probably do okay. the flat panel business is going through a boom right now, and apparently people are still slow to react. as long as the PS3 business starts recovering, they'll do more than okay. of course, bad things can still happen, like the chinese marginalizing the flat panel market. but sony appears to be selling on the back of quality once again, and that's something the chinese can't assault anytime soon. sony seems like it's starting to get back on its feet, but that's just my opinion.