How will ubuntu help you out installing xcode? Ubuntu is not the end all of things.
The "fad" of running things in a vm is so that you can validate that you've not forgotten something about your setup and deploy process. If you run it locally on your workstation that you've tweaked umpteen million ways you may have forgotten about some tweak you made and boom your deploy doesn't work. Fully automating a vm build and setup for local use helps work those kinks out. I'm not a web guy but do the same thing for my ec2 setups.
Also some of use prefer not to use Linux or Windows as our workstation. At work now I am typing this on an Arch linux box, but prefer osx for regular use primarily because of the less bs situation. In addition using windows for the base os means things like having to deal with stuff like cygwin/etc.... and their stupid peculiarities and quirks.