If something is already installed on a External HDD.. it shouldn't have to rely on registrys and permissions or whatever wacky system is has when moving from your original Computer to a laptop to play.
When I had Guild Wars installed, I could move that External HDD to different computer or laptop no problem, as long as it installed correctly on my External HDD.
FFXI Online.. on the other hand, wants you to watch paint dry for 10 more hours as it installs again for the 2nd time in a 2nd, different location.
Edited, Jan 29th 2013 8:37am by AlexFitz