As the article describes - logging, memory dumps, object cache, etc. consumes disk space and helps the farm be performant.
Also, 80GB per server isn't much in the scheme of things. You really don't want to have other services running on a SharePoint Server (due to the resource consumption, you want SharePoint to have all it can to help performance, especially so if you have a high number of users). If you have a server capable of running SharePoint 2010, it will be modern enough to have a large amount of disk space.
Having said this, my development systems never really go above 50GB - and that's everything (SharePoint binaries, SQL Server 2008 R2, Windows Server 2008 R2, Visual Studio 2010 Ultimate), 3 web apps, and that's with minimal to no content existing on the servers.