And that's all this while we're in the middle of a major architectural shift and hiring/interviewing like crazy (check out https://www.greplin.com/jobs! We're still hiring across the board).
The best part is that this is all nothing compared to the changes you're going to see in the coming months :-D
How is Mark an outlier relatively to the sentence you have quoted? He started from 0 and had nothing to show besides the flip flops on his feet and his skills.
The two arguable factors are luck and outside capital. Are you sure luck played such a great factor in his case ? and was his decision to take outside funding at that stage unnecessary?
How many people do you know who started off at an age of 19-20 and were a tech celebrity in 2-3 years? Well I do not know of many hence they are and will be an outlier for me.
A lot of things including luck and timing beside the usual clicked for both Mark and Bill and hence they are where they are today!