I read an interesting conversation about World of Warcraft “clones” (because I can’t say no to a topic I know will leave me steaming), someone brought up cars, and why no one refers to today’s cars as “Model T clones,” or “Ford clones” because Ford made the first commercially viable automobile. This got me thinking, and I found that cars do get compared just as much as MMOs do. Not all the way back to the Model T, but to one another, as “clones.”
Automobiles are, for the most part, structurally similar. They contain your basic engine, headlights, dashboard, steering wheel, four wheels, etc. Compared to an MMO, these would be the systems that make the game not unique, but are rather required simply to maintain functionality. Where vehicles start to branch out starts to come into effect when looking at the casing (graphics), handling (controls), speed (performance), reliability (long term viability), and other perks and pieces. For example, my Kia Rio looks a bit like my friend’s Honda, but while my car carries Sirius Satellite Radio, his car has fancy things like anti-lock breaks and electric windows.
What you end up with are automobile companies that are famous for one thing or another, each with a line of vehicles that are easily distinguished from one another from a visual and statistical perspective. For example, most minivans look alike, but when you look at them closely, you start to see the distinguishing features.
So perhaps the car analogy does fit well, but the same applies to any line of products, and I imagine I would see similar conversations going on cars if I frequented those forums the same way I do for MMOs.
MMO Fallout 
..and yet when a bargain car-maker makes a an obvious copy of the styling of a European luxury car, we do call it a “clone” or “copy.” Examples abound in China right now. The original Lexus LS is a classic case of setting out to build a Mercedes and ending up with a Mercedes.
So, what makes a game a WoW-clone? Aspiring to the exact same gameplay and UI. Thus, DDO, WAR, Co, etc etc etc are NOT WoW clones, but plenty of other games genuinely are.
I agree to the extent where the car’s aesthetics and performance are comparable. For example, a bargain-car maker might try to reproduce the design of the convertible, but in order to keep the car cheap, it lacks the powerful engine, the power steering, and overall handling. So rather than the car being known as a cheaper alternative, it becomes the crappy knockoff, much like the tPhone, oPhone, HiPhone, etc.
The best example I can give is Alganon. Alganon copied the look and feel of WoW (down to an almost copy and paste on the UI, landscape, etc), including how the game played. On the same note, the game featured none of what made WoW fun. No PvP, terrible lag, horrible server performance. And as a result, the MMO community rejected the title, to the point where David Allen was fired, the game went free to play, and the has been on the repair ever since.
Alganon attempted to be a WoW clone, and was rejected as a crappy knockoff for those reasons. The closest I can see coming to a World of Warcraft clone is Rift, because Trion has managed to reproduce the look and feel of WoW, while also maintaining the level of polish that Blizzard brought along with it.