To Rhye:
In the .dll source code:
CvPlot.cpp -> CvPlot::getUpgradeTimeLeft(....)
there is switch statement that is supposed to modify the cottage growth for the different civilizations. This is not working.
The getUpgradeTimeLeft function is used only for display purposes. I tested it, an Egyptian cottage is supposed to grow in 13 turns, however, it grew in 10. So in fact the current switch statement only has the effect of displaying wrong information.
To modify the cottage growth time is tricky business. Basically Firaxis' code is buggy. The growth time is 10, 20, 30 and the base growth rate is 1 per turn. Cottage Growth modifiers (or Upgrade rate) belongs to CvPlayer::getImprovementUpgradeRate(), however, due to integer rounding any modifier other than N x 100 percent has buggy effect. The correct fix for this, is to increase the growth requirement for cottages to 10000, 20000 and so on and increase the base growth rate to 100. I can give you the details of how to do that, if you are interested (it is easier than I initially thought it would be).