I see, so it was a matter of poor adoption and not restriction. It looks like I misunderstood the words "*Don't touch the release tags at all. Ever!*" on http://www.mediawiki.org/wiki/Commit_access page - they were just about MediaWiki releases and other tags a encouraged.
It's definitely makes a big difference for me as developer since not having a way to support deployment is a deal breaker for me.
I really prefer to have my extensions in MW repository - so the next question then is what are the guidelines for SVN usage for Extension developers (especially tagging so developers of code-rich extensions like Semantic Forms and Semantic MediaWiki can use it), and how does one get commit access to the repository ;) Also, can you guys import a project from another repository, e.g. Google code hosting (first two in line will be "Header Tabs" and "Widgets" extensions)?
Sergey