The 'best database' article recently linked here, says

"PostgreSQL picks a method of concurrency control that works best for high INSERT and SELECT workloads. [...] tracking overhead for UPDATE and DELETE."

This one says "INSERT and UPDATE operations create new copies (or “row versions”) of any modified rows, leaving the old versions on disk until they can be cleaned up."

I do think this one is wrong, but this is my wild guess as I am no expert in any way. INSERT should be fine. Or how would INSERT "create new copies"?

[Edit] See authors comment.