To say that Tony Gwynn, Jr's hit kept the Padres out of the playoff is ... well ... wrong.
Gwynn's triple only tied the game for the Brewers, it didn't win it. Additionally, that was only the penultimate game of the season. The Padres still could have won the last game of the season, which of course they didn't. Add to that, they STILL had a one game playoff with the Rockies ...
So, Gwynn's triple basically did as much to keep the Padres out of the playoffs as any other opposing player's RBI.