Of course, that short little bar that represents Oct 2005 -> Jan 2006...yeah, that's be when I bought my 20" iMac G5 w/iSight. The guides don't always work. The iMac line upgrade standard deviation is very large. I think they must upgrade the line every time Steve sneezes.
Depending on how they do it, a major new feature such as religion may not add too much to the complexity of the game. If you've played SimCity3, you'll know what I mean. They added garbage collection in addition to the earlier electrical and water distribution mechanisms, and it was something that was easily learned and handled. Civ4 may handle it equally nicely.