Obviously no player ever wins a title by himself, but a transcendant player doesn't require as much help as maybe others do. That said, the supporting cast definitely makes a difference.
The example I've seen used often in this thread is the '03 Spurs. That team makes a clear example of both principles in play. There were no other in-their-prime studs on that team, as they were all either too old (Robinson, Kevin Willis), too young (Parker, Ginobili, Steven Jackson) or in prime role players (Bowen, Malik Rose, Speedy Claxton). There was talent there but out of time phase, and Duncan was clearly the driving force. His play that playoffs was transcendant.
On the other hand, his teammates and the coaching scheme did take care of their business as well and keep the team in the position where Duncan could carry them. The one area where age didn't matter so much was on defense, and those Spurs were uniquely built to be difficult on the then-champion Lakers with lots of big bodies to throw at Shaq and lots of athletic/agressive wings to throw at Kobe. In that respect Duncan's cast has become underrated over time, because without that kind of team/scheme help, Duncan isn't in a position to beat the Lakers even with his high level of play.
Superstars can make it easier for their team to win, but even the non All-Star casts make big-time contributions to make it possible for a team to win a title.