That will be interesting to see if they actually release Office on Linux distros should the Linux desktop become more popular (and that's kind of expected).
They'll go where the money is. But its not been established that Linux is anything other than a services sector. So far nobody has managed to sell consumer software on Linux in a big way. Maybe some tiny games and whatnot here and there, but, Microsoft will (and probably should) ignore any market that won't bring in atleast a hundred million in revenue.