Think your perspective is a bit off there if you think this should be causing a stock meltdown or a mass exodus. Most people, rightly or wrongly, probably aren't all that interested in Microsoft's involvement, but more concerned about where Snowden is and whether he's leaking our classified information to other nations. Yes, there are people upset at the tech companies and the NSA, but I don't think it's nearly as widespread as it is in the tech echo chamber.
EDIT: To clarify, maybe this SHOULD cause a mass exodus in an ideal world. But I don't think that matches up with reality, and therefore I don't think a mass exodus/stock meltdown is really an expected outcome.
The people in charge of buying software and services buy what they are told to buy by their bosses. The bosses making those decisions oftentimes are uninformed and unconcerned with the things you might imagine that they would be.
EDIT: To clarify, maybe this SHOULD cause a mass exodus in an ideal world. But I don't think that matches up with reality, and therefore I don't think a mass exodus/stock meltdown is really an expected outcome.