As most of the people (Win XP/7/8.0 or upgraded from 8.0 to 8.1) already have .NET 3.5 installed this usually doesn't happen, hence there is no mention of this in the modpack. Python can do all sorts of things including calling upon a .NET framework API to handle requests and present these in an overlay. The use of such a way is completely up to the coder of any mod. I'm not saying this is the right way of coding, but it this specific case it happened to be a required feature.
I can't promise anything but I'll contact Aslain and ask if he would include a notion of the required framework in the description text. I do hope this is to your satisfaction :)