Dries Buytaert wrote a post analyzing the contributions to Drupal, and who sponsored them.
Despite the large number of individual contributors, a relatively small number do the majority of the work. Approximately 51% of the contributors involved got just one credit. The top 30 contributors (or top 0.5% contributors) account for over 21% of the total credits, indicating that these individuals put an incredible amount of time and effort in developing Drupal and its contributed modules.
The whole thing is very interesting. In some ways it mirrors what we see with WordPress, but in others it's quite different.
For instance, 69% of what they called “credited work” is sponsored by organizations, and the top 30 organizations made up 29% of total credits. That is actually — I think — I significantly wider distribution than what we see with the top 30 contributors to WordPress, period, much less from official organizational sponsorship. But I'd have to do much more research to confirm that.
The only analysis I know of isn't on props, but on commits, and that data showed that just over 81% of core commits are made by employees of six companies. Granted, there were only 35 committers when this was written, and it doesn't reflect the props — as in a much broader swath of individuals that worked on those projects — but it's still an interesting comparison. Aaron Jorbin has another post regarding contributor continuity, which is also interesting, but also not a direct correlation to Drupal's analysis.
I love Dries' analysis, and would like to see more of the same with WordPress. I think contribution as culture is really important for successful companies, and successful open source ecosystems.