Why a victory? Because it means the liberals won on the key points -- the exclusion of protesters from the public walkway was not content based restriction on speech and the state has a legitimate interest in protecting access to abortion clinics. What got struck down was the failure of the state to justify ON A LEGISLATIVE RECORD why it needed such large exclusion zones to achieve its purpose. The court appears to draw a road map as to how the MA legislature could go back and draft a statute that would survive intermediate scrutiny.
It is also significant to protest movements like Occupy because the legal standard means that "access to the public streets" is protected and the ability of government to limit access to these areas "traditionally associated with free speech" is limited.
Will need to read more thoroughly, but does not appear to be the total defeat supporters of the exclusion zone perceive it to be -- which is why you have the 4 "liberals" signing on to the opinion written by Roberts with concurrence from the other conservatives.
Link to decision: http://www.supremecourt.gov/opinions/13pdf/12-1168_6k47.pdf