Peter Mularien takes a look at the developers for Spring and comes up with an unsurprising conclusion: "the vast majority of development on Spring Core is performed by SpringSource employees."
Though Peter suggests he's not trying to make a judgment on this fact, he implies that this somehow impugns the "open source-ness" of Spring. Indeed, in a comment on Rod Johnson's blog, Mularien suggests that the employment of Spring's developers by SpringSource "begs the question of how open the APL-licensed projects really are to outside involvement and contributions."
I think Mularien may be conflating "open source" with "open employment." The two are not the same.
All open-source projects are developed by a small core of committers. In the "important" open-source projects, those developers are employed by a range of companies. The difference with SpringSource (and other commercial open-source companies like SugarCRM, Alfresco, MySQL, etc.) is that it employs most or all of the developers.
Is this a bad thing? More pertinently to Mularien's contention, is it "less" open source?
Not in the least.
Open source refers to licensing, not employment. The OSI maintains a list of approved open-source licenses. If my code is licensed under an OSI-approved license, my code is open source. Plain and simple.
The fact that Mularien might have trouble contributing to the core Spring Framework project is immaterial to whether the code is open source or not. He can always fork it. That is the true measure of open-source code - the right to fork - and it's a function of licensing, not employment.
Besides, Mularien's point, while valid, misses the larger issue: who is most likely to want to modify source code? Based on my experience with Alfresco, I'd suggest that Mularien look to SpringSource's customers for this answer. Organizations like FedEx, Aetna, NASA, etc. use the Spring Framework, and many of them likely modify it.
Is Spring less open source because such enterprise users modify the Spring source code without working for SpringSource? Nope. In fact, I suspect that they would struggle to care less.