Big or small company, I doubt they can pay the employees' salary with "exposure". They might have pratically infinite VC money for now, but that's an orthogonal discussion, just as "exposure" and being fairly compensated are.

edit: and what about it had been a smaller company or individual researcher who wouldn't be able to gain as much from this publicity? Are you saying that Microsoft would have awarded them $ 500k? Because that's not the message sent with this reward. And frankly, even this discussion is kind of off-the-point because I doubt that's what they took into account when defining the money quantity.