In the end the choice wasn't made for philosophical reasons. It was made because the robot library was in Python, or so he thinks. I think this actually shows there was a strong reason to never use Scheme: it's a failed language family. Outside of academic life support and very niche uses (which are usually directly caused by the academic uses, such as Emacs lisp) scheme just doesn't exist out in the world, despite a dozen very competent and complete implementations that are still supported. This is not an invitation for lisp fan boys to stomp their feet, TIOBE doesn't have any (()())()(()) language in the top 20. Debate rankings all you want, but lisp type languages are extremely rarely used because people don't find them productive when given a choice.
I think that’s key to understanding the issue, so I guess the conversation is over.
There is clearly a pedagogical/philosophical difference, and that is usually what is used to justify using Scheme.