Well, market cap can increase not only through share price appreciation, but also through new share issuance. In that case, shareholders dont gain much, except if the new shares are at high price. Like what happened in Reliance Power - Anil Ambani bought most shares at Rs. 10/- (average price of Rs. 15 or so) and issued the same shares to retail guys at Rs. 500 levels, thereby increasing book value to around Rs. 60 - 70 (quadrupling his net worth !), and with market price a multiple of that !!
It would be worthwhile to note that out of the billions of market cap, how much is share price appreciation, and how much new shares...