Even though it's hard to find any flaw in "Use the right tool for the job", I still think that the success of a start up in Silicon Valley (and probably the rest of the world) has a lot less to do with the technical choices of the company than the people who work there. And luck. A lot of luck.
It's still baffling to me that pg doesn't realize how lucky he was. He was in the right place at the right time and he was probably surrounded by competent technical and non technical people. If you have such a team, the technical preferences of the engineers will probably have very little bearing on the success of the company as long as they use the tools they are proficient with and which allow them to execute quickly.
I mean, the fact that Rails and PHP were at the origin of Twitter and Facebook alone shows that the quality of programming languages is irrelevant for the early year(s) of a start up.
Besides, assembly fails the "allows to execute quickly" test.
I'm pretty sure that what PG was trying to say was that given two languages X and Y that if X is more powerful (expressive) than Y it will be better for startups.
Not that if you don't use X there is no way your startup will be successful, and certainly not that if you don't use LISP you won't be successful.
I always thought he was speaking largely from survivor bias - "we succeeded, and we did X, therefore X must have contributed to our success."
My comment was couching against someone coming in later with a "well he really meant the right tool for the job."
Look at some of the largest tech companies and what languages they used to get big:
Probably not what PG would have had in mind.If you move away from his objective claim about Lisp's "power" to a subjective metric based on "the right tool for the job", then sure. (Though reading e.g. Hackers and Painters, his argument around Lisp was specific to the power of that language.)
PHP perfectly fits the "move fast and break things" mantra of early Facebook. Ruby allowed for quick iteration at early Twitter.
Note that Facebook built a PHP-to-C++ compiler called HipHop, while Twitter switched largely to Scala. Box (to the best of my knowledge) has supplemented PHP with Java and Scala. Github maintained a custom fork of Rails for a long time to achieve the performance it needed.
So no, it doesn't appear that Lisp-flavoured companies have an advantage.