Yes, what you said also apply to MySQL/InnoDB and MongoDB. Someone did an experiment with MongoDB some times ago for various id schemes: http://i.imgur.com/clm9D.png (https://groups.google.com/d/topic/mongodb-user/1gPqVmFHExY/d...), I don't know if Postgres is being different but people should do their own testings instead of blindly listening to advices from the Internet.
