From a game to game basis, the difference is indeed small, like several other things. But over the course of a season, allowing just 1 more HD scoring chance per game is going to mean ~10-20 more goals against. (the HD Sv% for goalies goes between 75% for the very worst and 85% for the very best, generally)
Goalies' numbers over a course of a season are meaningless. Game to game numbers are what important.