I can't give you a good answer. The default permissions are set by the developers of the individual distros. In practice you will see various permission sets from one distro to another, and even between versions. I guess it depends on how the developers see the distro being used. As you can see file/folder ownership and permissions are easily set so it doesn't seem to be a big issue.
Insanity: Doing the same thing over and over and each time expecting a different result.
Democracy is 2 wolves and a lamb voting on the menu. Liberty is an armed lamb protesting the electoral outcome. A Republic negates the need for an armed protest.