-May push for doing experiments and iterations that have been done and rejected before.
-May lead discussions towards and rehash things that have been settled before.
-May not be able to reason about how different pieces of the company fit together because, he or she will not be familiar enough with the details of these pieces.
It's about not having finely tuned error bars over facts and hypotheses about the company, about the missing non-commodity knowledge. I hate the words "tribal knowledge". However, I'm sure they thought about this. Joel Spolsky of all people, would understand these concepts.
Stack currently feels like an attempt to be the worst parts of both Wikipedia and Ask.com. They need to do a better job at something, and everyone will have an opinion about what the fix is, but it feels like they need a change.
That said, hiring a developer to run Stack sounds weird to me. If anything, I'd think you need a communications/publishing person since the goal is collecting, archiving and distributing data. Maybe an archivist or librarian even.
Are there many (or any?) cases of this having a long-term effect on a company's culture/focus? I know it's the most-advertised reason for hiring an outside CEO, but I couldn't find any examples of a company's culture changing, and staying changed for years/decades, as a result of doing so.
Seriously? I can understand the Wikipedia aspect of it (though I'm not sure I totally agree), but ask.com? Isn't ask.com full of trolls asking intentionally silly questions, and writing ridiculous answers? I fail to see how StackOverflow falls into that category.
Now there are cases where hiring an outsider makes sense. Perhaps you are bringing in someone with experience to run a fast-growing company and no one internally has that experience. Or you are hiring a new CFO for a tech startup and there just isn't a large pool of people to promote internally to that specific position. But given that stack overflow is a tool made by developers and aimed large at developers--and a mature company--it would be nice to see someone rise through the ranks from a developer position at the company to replace the CEO.