The reason people doubt it is that developers tend to group at skill levels. It's rare to have a 10x difference in a single shop or on a single team. But it's very common for the top dev at a top company to be 10x the worst dev at another company for any given task.

What most people forget is that the 10x figure only measured those who completed the task. For any given task, there are definitely 0x devs and devs with negative velocity.