While I was Adventuring around, I decided to go vampeer huntin, so I went to half moon mill, took out a Bow (glassbow w/ poisoned steel arrows) w/ x2 damage, killed her, looked for Hod(thats the husband right?) I saw a courier, walk right down the bridge, and informed me of hert's death(90 gold)
I should kill the courier too....

...Hell, I got a letter from a courier about a Dragon SHout location five seconds after shouting in town...
...Wait...
I bet it's him who's been writing those...

Or when you're in Solitude, buy a Dwarven weapon, and five seconds later a courier approaches with a letter from Calcelmo in Markarth inquiring about the weapon.

News travels fast in Skyrim, it seems. Maybe the courier just has all these letters on hand "just in case" and waits in the shadows for the chance to deliver them.

The other thing is, all these jokers in Skyrim ask me to deliver things for them... hey, buddy, ever heard of a courier?