Keep in mind the following observations:
1) Jeter is pretty sure-handed. You tend to notice errors and errors, but not missed plays, especially in the infield.
2) Jeter is quite acrobatic for his size. His jump-throw, his dive in the stands against the Sox, his flip toss against Oakland, i.g., are what fans remember.
3) He's been there for a long time and is very durable. I really noticed the difference when Alberto Gonzalez was the shortstop, but it's been 13 years that Jeter's manned the position. It's not easy to remember someone's range after all those years, or objectively critique the lack thereof of the current shortstop's range. It's not like we compare it to someone else with ease.
4) It's tough to see on TV. You see a ball hit up the middle, and it gets past Jeter. It's tough to see that another shortstop would have had it. The ball is hit, the camera angle changes, and the ball goes through. I see a lot of games at the stadium, so I see what other's miss on TV.
5) Defense is harder to quantify for most people. Most people can see that someone is a good hitter or pitcher. You can study someone's stance, or pitching mechanics, etc., It's harder to see how a player sets his feet, his positioning on defense. I don't buy the crap that most Red Sox fans "knew" Jeter was a poor defensive shortstop. They heard it from someone who heard it from someone who read a statistical analysis. To tell you the truth, I didn't realize it until a) I started going to the games regularly and I was told that statistical research back up the claim. I would have probably thrown it out myself if I didn't actively look for it at the Stadium.
6) It's Derek Jeter. That can't be overstated. He's the Golden Boy for most Yankee fans. That's like telling you that Varitek is a s***** game-caller. We know that, but many Red Sox fans refuse to see it.
So cut them some slack. When you think about it, you have a lot of better targets than this guy.