We looked at this in exhaustive depth about 6 months ago. This is only true if you back up just the database. Once you have to backup the database and the uploads too, it is unavoidable that you need to merge the database backup, which is one giant streamed-to-compression file, with a bunch of .jpg and .gif and .png and .doc uploaded files, so at that point you need 2x disk space and that 2x space cost is indeed unavoidable.
So, if disk space is at a premium, select the “database only” backup style, and back up the uploads some other way. Compressing gifs and jpgs doesn’t work very well anyway, so just straight copying them out is a viable strategy, minus “lots of tiny files” processing overhead.
cc @pfaffman