I'm on Gentoo for example. I can write an ebuild to automatically download said deb, extract it, install it with the package manager... And if the site has any semblance of organization involved, I can write one ebuild that will always download the version specified in its name, so when there is an update, I can copy the ebuild, change its name to new version and if the dependencies or structure didn't change, it will install just fine without any work.
I am quite comfortable finding my way around ArchLinux, and recently decided to give Gentoo a try. I didn't expect it to be that much harder but all the cflags, emerge, conflicts and updates feels like black magic. I guess that if you know your way around Gentoo, reverse-engineering a deb file is not a real challenge. However I'm assuming that most Linux users would hope for a less involved solution.
Stability, slow changes, predictable, strong history, lots of distributions are based on it, the list goes on and on. I don't use it but it's kinda stupid to question it's relevant qualities considering how much it's brought to the Linux community.