I will not go into any conspiracy theories (at least not too much), but it seems to me that there is much more to this story than can be read publicly. If the FSB got involved in everything, then there was a good reason. Did they just decide to be good guys and stop some illegal activity, or they didn't give FSB their share of the cake?
Probably they decided to get their hands on those coins before somebody else does, knowing that sooner or later the whole thing will turn just like btc-e , so why not grab it and act like is an act of justice against <insert enemy here>?
Highly ironic, especially if you check the older threads two years ago when their supporters were shouting btc-e/wex can't be shut down, this is Russia, etc etc.
YoBit is also a Russian based company, but I don't see them having any problems from the Russian authorities. Are they paying for protection, or just not engaging in illegal activities?
Probably a combination of everything and something on top of that pile, maybe they are even outside of the reach of the FSB, operating from god knows where and paying that protection fee to somebody else. Or, maybe it's the FSB running it and they disposed of wex? No amount of tinfoil is enough for what's happening there.
Either way, shady as fword, and will probably have a just as shady end.