The great thing about having star players, and the thing the OKC Thunder have been depending on all season, is that those players are able to elevate their performances for the postseason. For the sake of argument and example, take the career and playoff splits of these three players.
Regular Season: 23.0 points, 6.6 rebounds, 8.2 assists
Post-season: 25.1 points, 6.7 rebounds, 7.9 assists
Regular Season: 18.6 points, 6.2 rebounds, 3.2 assists
Post-season: 19.3 points, 7.2 rebounds, 3.9 assists
Regular Season: 27.2 points, 7.4 rebounds, 7.2 assists
Post-season: 28.5 points, 8.9 rebounds, 6.9 assists (my god)
As you can see, all three of them have excelled during the playoffs.