Orbitz tackled a hard technical problem with Common Lisp. I don't know if it was the "secret weapon", but it must have been fairly critical. They needed efficiency.
Viaweb is not even an example of that. They're a startup that succeeded while using a niche language. That's correlation, not causation, despite everything pg says.
I always thought dabbledb[1] was a good example of choosing Smalltalk. Sadly the product died, after the team moved to Twitter.
Still not sure why they didn't just open up the source.