AFAIK most of minificators also shortened variable / function names - are there any that don't do this? (take a look at minified jquery.js for instance)

minification can't (usually) happen on the public side of the API - that could explain jQuery, as a very large amount of it is public.

Otherwise yeah, you can just run it through a whitespace-remover. There are also often options on e.g. the YUI compressor: http://refresh-sf.com/yui/ and Google's: http://closure-compiler.appspot.com/home

Css get minified by removing whitespace because the keywords are important.. Javascript can have some magic done to it to reduce character count because only the consistency of the keywords matters.