Well I think you're both a bit incorrect...
The share price, and hence capitalisation of any company, is entirely controlled by the Market Makers, in the same way that the Course Bookie controls the price of a horse.
They use all sorts of factors to decide when to raise or lower the price of shares, including prospective future earnings, market news, possible bids, stake building and buys and sells.
But ultimately they are in it to make money, if raising or reducing the SP makes them the most that is what they will do.
And, same as the course bookmakers, they have to take account of what each other are doing to ensure that they have a competitive price for buyers and sellers.
That's my take on it anyway, :)
Happy New Year!