The miners are threatening these things, not doing them. Let's just see where their big-talk leads, besides, we already have effective ways to defend against these attacks anyway.
Evidently they only stopped short of carrying out their nefarious intentions, because the exchanges were able to put up a fight and made it quite clear that the world can always do without a best man! In the absence of that check, those miners were far gone on punching a hole on Bitcoin. Centralization of miners is a misnomer for Bitcoin, whose major selling point, is its decentralized nature.