This is known as typo-squatting and is not always done accidentally.

An interesting related technique is known as bit-squatting where you register domain names of a target company 1 bit different from the original.

It can be used for receiving emails, phishing sites, capturing internal DNS requests that have gone rogue due to bit errors (due to anything from hardware errors to cosmic rays).

There is a really good talk by Artem Dinaburg from Blackhat about it (first talk about it? I think) https://media.blackhat.com/bh-us-11/Dinaburg/BH_US_11_Dinabu...