This is a known matter. From what I’ve been told in the past, while Usermin is often released earlier on Webmin.com, it is vetted more before being released into the repo on Virtualmin.com.
It’s all good. If you notice anything that seems out of the ordinary, it’s perfectly fine to question it. Asking this type of question is never a waste of time, as I myself asked this question long ago myself since it seemed odd that the release date between sites was different.
That said, sometimes the repos don’t get generated correctly, meaning a package that “should” be available gets held back unintentionally, so again if you notice that there’s been a long delay in releasing a new version of something, definitely ask the question.