Having a runaway hit isn't just about creating it, but also successfully maintaining it. Strachan abandoned Apache Groovy only 2 years after creating it so he doesn't really count. Unfortunately he let in someone without any programming aptitude into the Codehaus despotry, and was eventually eased out with stirred up conflicts like the one over builder syntax in Dec 2005. He even had his commit privileges stripped from him afterwards.
On the contrary, I think, there are quite a few of them still. Just look at people who created Python, Emacs, Vi, Sublime Text, Charles Proxy, Nginx, Apache Httpd. And this is just scraping the surface of the useful software in the OSS.
May be percentage wise, they are less. But even a .1% of millions, still makes it in the 1000s. And lot of others who perhaps have the potential, but sadly never realize it.
James Strachan brought us Camel and Groovy. That's pretty good.
Gavin King had Hibernate and Seam. Not too shabby, either.
There are definitely people who are very good. To me, having more than one runaway hit is a good indicator.
But there are a very few of them.