Then just wondering why wont VirtualBox create a ppa that can be added using something like `add-apt-repository ppa:virtualbox/ppa` instead of downloading keys manually (I know its easy enough). But isit ppa a more convenient way to do things?
And a PPA depends on Launchpad. Something Oracle does not like. Hence they made their own debian repository, because with that, they can't just serve Ubuntu users, but Debian as well, and RPM based distro's, all on the same server. That is something that isn't easily possible with Launchpad.
That is just a configure switch that one can enable. Oracle build their version without it to avoid conflicts when one installs the ExtPack which provides VRDP.