Right now there is probably a game design professor from your average tertiary education institution out there somewhere sitting back, smiling smugly to themselves getting ready to prattle on about concepts such a scope creep and how ol' Sid is pretty much just quoting something from design 101...
But anywho - as many have already mentioned it's about the balance really and a game like Civ does not need to be anymore complex to be fun, in a way, keeping the complexity down whilst either maintaining or increasing the challenge and depth is one of the hallmarks of a great designer and I think when it comes to this kind of fine tuning Sid really is the ultimate master here - so it's probably worthwhile to take that into consideration (along with extensive notes perhaps) before we humble masses start up the wild uninformed speculations of "dumbing down" and "cutting features for future DLC".
But anywho - as many have already mentioned it's about the balance really and a game like Civ does not need to be anymore complex to be fun, in a way, keeping the complexity down whilst either maintaining or increasing the challenge and depth is one of the hallmarks of a great designer and I think when it comes to this kind of fine tuning Sid really is the ultimate master here - so it's probably worthwhile to take that into consideration (along with extensive notes perhaps) before we humble masses start up the wild uninformed speculations of "dumbing down" and "cutting features for future DLC".