What they're doing is forcing a disassociation upon someone. Isn't that exactly the same as disfellowshipping?
From what I can see, it is exactly the same thing. However, it certainly sounds better to the "world" if the Society can state that a person who takes blood has made the decision to leave the JWs himself. They've been taking a lot of flak from the media about excommunicating a person for taking blood to save their lives.
This "disassociation" claim sounds much better. In this way the WTBTS is absolved of all responsibility for abandoning the invidivual...it is now made to look as if the individual is the one making the decision.
Once again, it's all about how the WTBTS is perceived by the "world". This has always been their major concern...not the so-called "sheep".