Most of these are geographic rivalries that would have taken place otherwise. Boston/Montreal is old school and has nothing to do with the playoffs in the 80's. Edmonton/LA was because of a trade. If Sidney Crosby got traded to say, Buffalo, the Sabres and Penguins are going to have a heated rivalry. That's how it goes
Boston-Montreal played 9 straight seasons in the playoffs from 1984-1992 and then again in 1994. That's the kind of thing that builds a rivalry. Their rivalry began because of their repeated playoff matchups way back in the leagues infancy. Same with Montreal and Detroit in the late 50's, where they played each other in the finals almost every year.
The Miracle on Manchester happened long before the Gretzky trade, as did their series in 85 and 87. That trade added notoriety when they played each other in 1989, and they played each other in 90, 91, and 92, and the Kings knocked the Oilers out of contention in 93 in the regular season.
These were all rivalries that got to build and escalate because of matchups happening every year. Geographical rivalries occur BECAUSE they are in the same division, which leads to repeated games and a familiarity. Detroit-Colorado was one of the biggest rivalries of the post-divisional playoff era, and it was because they played each other in 96, 97, 99, 00, 02, etc, and it got bigger as it went. They have no proximity. Geography doesn't mean much to the players on the ice. Geography is more of a rivalry for fans.