Note that maybe some of the options listed here are not available for you. It depends if your kernel is offering this functionality or not.
When you set an option to default, it doesn't mean that as soon as you get out of linuxconf, this option will return to default value. Linuxconf has no way to know what are the default options of your kernel. It means that when you set an option to default, Linuxconf will not intervent in this option anymore, no matter what it is set to. Remember that kernel options are usually set in the /proc file system and, as this file system is mapped in memory, everything will be reset when you shutdown your machine.