DRM is common, and it never works. Valve's single player games are as easy to pirate as anything else. Has there ever been a single player game where DRM succeeded?
After this period, however, the DRM serves no purpose other than to frustrate legitimate buyers. Ideally, the game creators would disable the DRM after it has served its purpose, thereby eliminating problems for their customers as well as freeing up server resources and support call costs. Unfortunately, there are few companies willing to do this.
The expansion pack added a phone-home "feature" or alternatively DVD checks with a message box you had to click away every time you start a game or return to the menu. (if you don't have an internet connection or block its attempts to connect)
A recent patch has made this even more annoying by alternating which disc it wants and under certain circumstances appears to completely stop working if it can't phone home. Great when their servers go down.
Ugh. I'm sorry, that kind of user experience just doesn't cut it.
When the code executes on a remote server, however, you have a completely different kettle of fish.