Back in high school, when we were reading The Odyssey, our English teacher explained to us that Homer didn't actually "write" the epic poem. Strictly speaking, no one from Homer's era wrote the poem: It was recited. But even in the sense of composition, it was not, she explained, strictly accurate to say Homer wrote the story. What he did was stitch together various versions of the stories of the Trojan War and Odysseus' journey home (and presumably other tales lost to antiquity) into coherent wholes. In a sense, Homer was sampling. "Rosy-fingered dawn"? He probably didn't come up with that one himself.
I've found myself noticing a lot of tropes in the newspapers these days: words, phrases, factoids that writers or editors feel compelled to mention in every story about certain topics. For example, since Oscar Pistorius, the legless South African sprinter, was arrested for killing his girlfriend, every story about the case mentions that Pistorius was born without fibulas. A salient point? About Pistorius, sure. But in the context of the murder case, which skeletal components the man was or was not born with seems of little relevance.
Slightly more reasonable is the constant reminder that many Afghans go by a single name. True, anyone who has ever perused a newspaper article about Afghanistan should by now be aware of this fact. But one never knows when a first-time reader will wonder why the article "failed" to provide an Afghan warlord's surname. Now, if someone would just explain why the one name Afghans go by is almost always "Habibullah.". . .
And if Detroit added one resident for every mention of Detroit once being the United States' 4th largest city, Detroit would quickly become the United States' third largest city!
At what point does a trope become a cliche? Probably when it's been blogged about.