You might have used a site in the past that moved to a new domain, or you might just have a really awkward search history. There are good reasons for removing your autocomplete entries, and you might want to do so without deleting your entire search history.
And you dont have too either, just mark the bothersome entry and press SHIFT + DELETE to remove it.
An excelent example is the site kickass.so that recently moved back to it's .to domain due to some legal issues. It's so stressing to reach the wrong url when you just want to download an old linux distro in a hurry!