Cannot say enough about the common sense of any stock exchange not using Windows. And as London joins the stock exchange in NYC (USA) with the switch to Linux, I am willing to bet Microsoft is none too happy about the matter.
Besides cost and speed, there is also the matter of security. Seriously, how frightening is to actually trust an OS that defaults everything to administrator users for anything mission critical? It’s just as foolish as it was years ago as it is today.
And at the end of the day, it would be a little weird having the NYC stock exchange being run by a product that has its code closed from the public, running the very thing that allows people to buy and sell Microsoft stock. This point alone, makes the idea of running Windows a bit of a problem depending on the exchange in question I would think.