Okay, so since 1970:
1970 - Brazil - Felix
Not really considered a world-class keeper
1974 - West Germany - Sepp Maier
One of the best goalkeepers of his era
1978 - Argentina - Ubaldo Fillol
Probably one of the better keepers at the World Cup, but not generally considered a world-class player
1982 - Italy - Dino Zoff
One of the best keepers in the world at the time
1986 - Argentina - Nery Pumpido
Not considered a particularly good keeper
1990 - West Germany - Bodo Illgner
Not considered that great before the World Cup, but his stock rose dramatically after it
1994 - Brazil - Claudio Taffarel
Generally considered quite a weak keeper, certainly not world-class
1998 - France - Fabien Barthez
Eccentric, but generally considered a very good keeper
2002 - Brazil - Marcos
Had a good tournament, but had not been thought of as a particularly good keeper before that
2006 - Italy - Gianluigi Buffon
Best keeper in the world at the time
2010 - Spain - Iker Casillas
Best keeper in the world at the time
So I make it that of the last 11 World Cups, four were won by teams with a genuinely world-class keeper, three were won by teams with "good" goalkeepers, and four were won by teams with goalkeepers who were considered distinctly mediocre. So I don't really accept the premise.