Hm, tricky one to reply...
Because you quickly descend into the "when does history start" discussions.
For yesterday's history, you have a multitude media (newspaper, internet, TV,...) to provide (hopefully) a multitude of sources.
For older history, resources are much more reduced and more often less accessible. And sad but true, most people only go for the first site in Google. And more than often this first site is Wikipedia...
But then again, who says that the website with the "wrong" info is wrong after all
Kris