Those examples are details that identify a specific character. If you see a man with a cigar speaking intellectually to a guy he addresses as Watson, you think, ah, that must be Sherlock.

A trope is a more universal idea or object. A sidekick in general, or a cape, makes you think, a, that person must be a hero of some kind. Waving a wand and saying Abracadabra? Obviously a wizard. It's the use of something familiar to help you, the reader or audience, make conclusions about your story. TV uses tropes frequently because they often don't have time to deeply develop their characters or storyline.

Cheers,
Michelle