Upgrade In-Place was Availble Long Before Apple Lion
Lots of comments today WOWing before the majesty of Lion upgrade... Look, mah, no DVD! As long time Debian developer Bdale Garbee put it "the idea that you should have to reinstall from scratch on a new OS revision is sort of an aberration in history, foisted on the world by shrink-wrapped software suppliers with motives other than technical..."
Most BSD systems had a fairly rudimentary way to upgrade themselves 'over the air' with the command "make world & make install" and old hackers could even remember Vax had similar capabilities, too.
It was Debian GNU/Linux that made the concept of distribution upgrade popular and very user friendly. All you have to do to upgrade any Debian system is type one command: apt-get dist-upgrade. Debian's release notes mention an automatic upgrade tool dselect for the first time on Debian GNU/Linux 1.3 release notes, dated August 11, 1997
More recently, upgrading any GNU/Linux distribution without a DVD and from a live system is the norm and I wouldn't expect less. After all, isn't Apple's App Store an imitation of Debian's APT repository or Fedora's RPM package archives?