The assertion of Papal supremacy by Gregory VII had a very different outcome from that of Boniface VIII. Why? Was the logic or religious justification different or was it just the times that had changed?
Context becomes particularly important in responding to this question. As both #2 and #3 make clear, one of the differences between these two acts was the way in which Boniface's measure was an attempt to bolster up the authority of the Papacy in the face of increasing independence of nations and unwillingness to see their power whittled away by the church. This is one of the central reasons for the differences between these two similar acts.
I would argue that it was more a change in the times. By the time of Boniface, there was much less willingness to defer to Church authority. The power of various nobles in Europe had become much more cemented and the Church was seen more as another contender for temporal power rather than as a purely spiritual force.
Gregory VII championed the cause of celebacy for priests, and argued that people did not need to follow the teachings of priests who were not celibant. Boniface VIII, on the other hand, felt that people could not be saved if they did not subject themselves to the teachings of the Pope.