Just about all podlings start off with all the initial commiters being on the PPMC (I only know of one case where that didn't happen).
One of the reasons put forward for not automatically making all new committers also PMC members is that it can lead to it being harder to make people committers. Some projects make it very easy to be a committer and grant it to just about anyone who seems like they are willing to do some work on the project without requiring any history of contributions. Examples of that are Apache Subversion's partial committers or many projects give GSoC students commit access when their GSoC project is accepted so they don't have the burden of submitting patches. Those sort of new committers probably don't have much knowledge of things like ASF release requirements and that can be a put off from making them a PMC member with a binding vote. ...ant
