So, I just have to rant about this.
I get annoyed when I'm skimming through RPG forums and see topics like "what's a good system for [SETTING]?" Not just because, more than half the time, they don't put the setting name in the subject title, so you have to read the post to see what the thread's actually about. And not just because people swarm in and name their favorite system, regardless of relevance, until eventually every possible game system has been mentioned, making the thread completely useless.
No, it's the very idea. Some guy says, "I want to run a campaign in the world of Mr. Ed" (or, more likely, "Mr. Ed, but with ninjas".) The implication being that there's some perfect system out there that will emulate "Mr. Ed" (with ninjas) better than any other system... and furthermore, that proper gamers should own and familiarize themselves with as many different RPGs as possible, so that they are prepared to play the proper system for any imaginable setting, without the risk of playing wrong. And therefore, designers need to keep designing games, in case someone comes up with a new setting that can't be matched to an existing system.
This is all the worst possible BS.
Really, matching a system to a playgroup only consists of two things: matching the broad style desired, and matching the system to the playgroup. You don't pick a game because the book lists all the things your desired setting contains; you pick a game because you're familiar with it, or it looks like the kind of game you could get familiar with. You don't pick a game that matches trivial background details of a setting; you pick a game that fits the general style you and the other players want to play in. As a crude example, there have been several official and unofficial Star Trek and Star Wars RPGs. Which one is the best? The actual setting is irrelevant; you could play Star Trek (or Star Wars) in a gritty, realistic way, or a loose, cinematic way, or in many other ways. You could play it with a d20 mechanic or a dice pool or with diceless bidding, resolving individual tasks, broad dramatic goals, or anything in between. You could use point-buy character creation, random rolls with a minimalist stat structure, or light freeform characters. The point is: you pick your game based on the kind of game you want to play, not on setting details. You can adapt existing mechanics to fit the setting details, or even borrow mechanics from another game entirely.
So, what people should be posting is: "I'm going to play in the Mr. Ed setting in a really light style that focuses on comedic switches in the storyline instead of tactical or realistic details. But I don't know anything about the light, comedic, story-driven games out there. Can anyone explain the differences?" (There'd still be replies like "You should use GURPS." But they'll be easier to spot and then ignore.)
Or: "My group uses Chivalry & Sorcery exclusively and doesn't want to learn a new system, but we've got an urge to play a Star Trek game. I need equipment lists, but want to do as little work as possible. Are there any good Star Trek-ish equipment lists out there for a game close enough to C&S that I could use them almost as-is?"
Or maybe even: "I'm going to use InSpectre's concept of earning mission dice in a D&D game. Anyone have any experience doing that? How did it work out?"
Don't give in to the tyranny of the perfect system. Find the games you and your group enjoy, then adapt other stuff like crazy, as needed.