At many positions there are distinct tiers, but distinguishing between players in those tiers is largely impossible. A perusal of the Dewan Fielding Bible gives us a few reasons why. Some infielders (like Derek Jeter) may be very good at getting to ball to their right, but very poor at getting to balls on their left. Some outfielders (like B. J. Upton) may be great at tracking down deep fly balls, but merely adequate on balls hit in front of them. Some first-baseman (like Mark Texeira) are great at footwork around the bag and corralling errant throws, but aren't great at throwing themselves or ranging away from the line.
Frankly, evaluating players on other teams (which is essentially what the Gold Glove ballot demands) isn't a manager's job. He worries about his team and, to a limited degree, his current opponent. The range of the guy playing third base for Kansas City should not be among his considerations (unless he manages Kansas City). As a result, at the end of the season, when he is called upon to vote on the Gold Gloves, the manager's choices are going to be skewed heavily by two factors: 1.) reputations and 2.) the small sample size of games played against his team. If Torii Hunter made a game-saving catch against his team in July, you can be damn sure that's going to weigh heavily on a manager's mind when he's filling out his ballot in October. But, let's face it, almost every centerfielder in baseball is going to make a few spectacular plays over the course of a season. These are all great athletes after all. The highlight reels aren't necessarily an accurate reflection of exceptional defense. There are balls that Franklin Gutierrez catches with ease that land Jacoby Ellsbury on Baseball Tonight. When Jeter makes that patented jump throw deep in the hole, Rafael Furcal has his feet planted and is uncorking his rifle.
Managers are, undoubtedly, going to be prejudiced towards players who they've seen a lot of, either because they play in their division or because they are veteran stars who have been around for a long time. In the last nine seasons Ichiro has made an impression on everybody with his consistency, speed, and powerful, accurate throwing. One could easily surmise that the manager for, say, the White Sox, who only see Seattle six times a year, might just assume that Ichiro did this season what he's been known to do in each of his previous years (remember when Rafael Palmeiro won a Gold Glove at first base even though he'd spend the entire season at DH). Rob Neyer argues, similarly, that Gold Gloves are impacted as much by a player's offensive contribution as their defensive one. Again, it is human nature to exaggerate the perfection of those that we admire. Derek Jeter and Joe Mauer are great hitters and (in many opinions, at least) likable men also, so it follows that they must be exemplary glovemen as well, right?
When I take umbrage with the Gold Gloves, it isn't so much with the voters as with the voting system. In a perfect world, who should determine the Gold Gloves? The BBWAA? The sabermetricians? Me? No, I think it would be in the best interest of the award if it was voted on by the General Managers. Think about it. In the contemporary era, front offices are increasingly concerned with a wide variety of player evaluations. They are expected to identify and objectively evaluate players from the whole league, so as to be prepared for trades and free agency, and so that they have a sense of the changing "market" of baseball (for instance, if the league is full of slick-fielding second-basemen, one doesn't want to overpay for one). If a GM were to spend several hours (or even several days) filling out his Gold Glove ballot; if he demanded some opinions from his staff of scouts and statisticians; if he watched a few reels of film, etc., etc., he could say with great confidence that knowing who the best defenders in baseball were was a significant and productive piece of his offseason preparations.