Because Bitbucket appears to be a high-traffic, high-maintenance website, and because there are many issues, bugs, feature requests, etc. that a single Admin cannot handle, it makes sense for Jesper to allow for community contribution to the codebase.
This would let users (and me!) to modify the code, add features, etc. upon approval by Jesper.
Of course, this necessitates Bitbucket to become open-source, or at least, conditionally open-source (possibly limited to select contributors).
The process of submiting code for approval, and the approval of that code, is to be determined! Hopefully something will be put in place. :)