Does chicken really have such a universal flavour to it? How did this come about?
There’s a big difference between supermarket bought chicken and corn fed free range chicken.
And I don’t just mean the price 
I’ve eaten a lot of strange critters, and many of them do bear a superficial resemblance to chicken. Alligator, which in Northern Virginia has become an underground Vietnamese delicacy, is similar, but tougher. I’m pretty certain it really was alligator tail I was eating–I’m friends with the chef.
Conversely, when I was in New Zealand I tried muttonbird, which as the name suggests tastes remarkably like sheep.
I’ve heard that it’s because it has such a mild flavor, that what you’re tasting is basically just bland protein. It’s not even restricted to the animal kingdom; sauteed shelf-fungus (you have to sautee it or it’s too tough, but it’s not poisonous) tastes remarkably like chicken, too.
Didn’t you ever see The Matrix?
“Maybe they screwed up, and couldn’t figure out exactly what chicken tastes like, and that’s why chicken tastes like everything.”
Much of the flavor in Beef and Pork that makes it taste unique comes from fat. Chicken has so little fat that its taste is not influenced by fat, or as chronos said, plain bland protein.
I heard it the way Chronos and tbea925 did. Remember that most wild animals are very lean, as are chickens. Most domesticated meat animals have been bred over the millennia to be genetically prone to be fatter and hence tastier. Also, their diets are designed to make them fatter. Not all wild animals taste like chicken, however. Bear is said to taste like pork; wolf and lynx are said to taste like mutton.
I don’t like eat chicken that is without the right amount of seasoning.
Crocodile tastes pretty much like chicken too - you can even get crocodile nuggets!
Don’t be fooled! Squirrel tastes nothing like chicken and neither does rattlesnake.