Modify default settings for subdivision surface modifier In some other 3D packages, like XSI, subdivision surface can be directly interacted with by default. It is possible to display a cage and modify that cage, but it is not mandatory. I have seen some Blender videos, such as this one, where something similar is being done. I notice three things:


Wire and Draw all edges are turned on by default for objects.
Optimal Display is turned on by default for subsurf modifier.
Mesh elements can be directly selected from the subdivision surface and there is no cage visible.


How could I set these as defaults in Blender? Do I have to write a Python add-on? Is there an example that I could look into? Intuitively, I feel this should be a popular requirement.
The video you linked to is a tutorial for the Sensei addon, which is a free addon that you can download and try. You will notice that the Sensei addon replaces a lot of the blender UI so that it's own operators are used, which is how the various defaults are different than blender's defaults.

Like the Sensei addon, you can create your own addon/s that perform tasks with your settings. You can start by creating an addon that defines an operator which adds a subsurf modifier with settings you want as well as turning on the draw wire settings for the object. This can be then be added to existing menus or custom hotkeys. To learn to create addons start with a Python tutorial if you don't know Python yet, then go through blender's addon tutorial.

Some code to put into your operators execute() method could be something like -

# bpy.context.active_object is needed if you test this script
# inside an operators execute you only want context.active_object
obj = bpy.context.active_object
# objects draw wireframe settings
obj.show_wire = True
obj.show_all_edges = True
# add a subsurf modifier
m = obj.modifiers.new('Subsurf', 'SUBSURF')
# this turns on optimal display
m.show_only_control_edges = True
# this shows the edit mode vertices on the
# deformed mesh not the real vertices
m.show_in_editmode = True
m.show_on_cage = True