I am not sure where these myths come from, but someone asked Google's John Mueller in Friday's Google Hangout on Google+ at the 11:15 minute mark if it is something Google may penalize for if the site doesn't link out to other sites. The person said they heard Google issues penalties when site's don't link to other external sites.
John Muller from Google quickly said there is no such penalty.
The question asked was:
I heard that there is a penalty if I don’t link out from my domain to different domain from any of my pages. Is that truth? Is not linking out from any of my page harmful?
No that's not correct.
So there is no penalty for not linking out, that's definitely not the case.
Obviously for users sometimes it makes sense to provide references and other websites that they can visit to to get more information on certain topics. So I think from a user experience point of view it's probably a good idea to have links on your pages.
But surely from a web spam point of view, from a Google indexing point of view you don't need to to put links on your pages.
John added his personal thoughts saying:
So I guess for me from a personal point of view, I really like to see links on other pages because it really kind of helps to keep the web a vibrant and that people go off and visit other things from time to time and they want to see different view points for the same type of information so that's something I certainly wouldn't suppress.
Which echoed what Gary Illyes said in a more "PC" way, where Gary said it's stupid not to link out and it makes him angry.
Here is the video embed:
Forum discussion at Google+.