I can appreciate how the notion that "save percentage isn't reliant on the team in front of you" is ludicrous. we watch enough hockey where we say things like "nobody could've stopped that because the d-man fell down or was out of position."
the point is, this happens on an equal enough basis both ways - (the opposite side is a breakaway where the guy just puts it in the crest) where it should even out. the same goes for high shot counting arenas and low ones. Over the course of a season, the truth usually bears fruit in the save percentage number.
if anything, bad teams giving up a lot of shots should HELP a good goaltender's save percentage because while his team may be giving up more shots, the opposition is going to have average shooting percentage of the league. So the goaltender is making more saves of the same type - his save % should be higher.
many of us like to use the "eye test" instead of stats and our eyes tell us that there are many occasions every game where a great chance doesn't result in a goal - many more than where a goal is scored.