How many games require you to be online, now? I know Blizzard was doing that, but those are games I wasn't going to buy, anyway. I have played all the SimCity games prior to this, as the first four Civ games. Now, I have to go look closely at CivV to make sure it doesn't have this requirement.
What really concerns me is the ongoing support. I still have the second, third, and fourth games of each series, and I like to pull the old ones out every once in a while. It's tricky, but not too difficult, to keep a Windows 98 machine running for the oldest ones. I just have to make sure I don't go faster than a 300Mhz PentiumII processor. The thing that I'm now worried about is the third games. I can make SC3K work in Windows 7, but I haven't gotten Civ3 to, yet. What happens when Microsoft stops all support for WindowsXP, and I can't authenticate a new install, anymore?
tl;dr version: If you have to be online to play the game, the manufacturer/distributor/publisher/etc. has to have something on the other end. How long can we count on that being there?