Answers From The Civ IV Team
Yeah, I agree this solution is far from perfect, but the problem is that publishers/game makers want their DRM, and they've been having it for years.
Another solution would be a steam like online authentication service, you can have multiple installs, but can only play at 1 computer at a time. It will come to that eventually I am sure, but right now there is still much against it, because alot of people play single player games without internet. And alot of people still have something against online verification, not to talk about the the technical issue's of failing/unreachable authentication servers