The NHL playoff Goal Leader for 2011 was Boston's David Krejci who tallied 12 times. During the regular campaign he scored only 13 times over 75 games. This is one of the lowest regular season goal totals for a player that would go on to lead the playoffs in goal scoring of all-time.
Prior to Krejci, the most recent unlikely playoff goal leader would have to be Edmonton's Fernando Pisani with 14 in 2006 after a regular season of 18 goals. Krejci just about accomplished a rare feat of scoring as many or more goals in the playoffs than he did in the regular season. This in fact did happen three times over four years in the mid-1990's, mainly due to the fact that the players had played far less than the full amount of regular season games.
Sergei Fedorov led the playoffs in goals with 10 in 1998 after scoring only 6 in 21 regular season games. In both 1997 and 1995 Claude Lemiuex led each playoff with 13 goals, during seasons which he scored only 11 and 6 goals. However he only played 45 games each season due to injuries. As well, in 1993 Wayne Gretzky led the playoffs with 15 goals in a season which he only scored 16 times; he like Lemieux however had played in only 45 games during the season.
In reality it has been over 50 years since a playoff goal leader had even close to his regular season goal total in a year which he didn't miss a significant amount of games.
In 1959, Montreal's Marcel Bonin led in playoff goals with 10 after scoring only 13 in the season. Even Bonin though missed 13 regular season matches, playing in 57.
In 1953, Boston's Ed Sanford scored 8 playoff goals to lead the NHL after potting only 14 during the season, he as well though missed 9 of the 70 scheduled games. Hank Goldup of Toronto equalled Fedorov and Lemieux's low of 6 regular season goals for a playoff leader. Rookie Goldup led with 5 playoff goals but had played less than half the season with the Leafs in scoring his 6 goals.
It seems it's safe to say that David Krejci would have to be the most improbable playoff goal leader in modern times (post 1940) barely narrowing out Pisani for the "title".