Earlier quoted context omitted.
I don't know what they save but 10GB is surely not purely saved games. It's those games fault not about 'saving saved games by default'.
Nope, Witcher 1 saves are just really large (for some reason in addition to all the flags they also contain some locale data and such). 10GiB is actually pretty reasonable for a Witcher playthrough.
In the witcher 1 there is also an uncompressed BMP thumbnail with each save that is about a megabyte. It's PNG compressed in the witcher 2. They learned from their mistake.