Your problem didn't had anything to do with Couatl or the Addon Manager or the installer.
Your problem was caused ONLY by too many people downloading the updates, which caused by the slow downloads and possibly the missing files alert (files were not missing, it was just a server timeout), which are now probably too much to handle, even for our TWO server mirrors.
We are already working on this, of course, and the next update will download from Amazon S3 Web services so, basically, it will be impossible to bring it down, even on a new release, and the speed will by MUCH better.