Ubuntu is (almost all parts anyway) free in exactly the way the Free Software Foundation defines the word. Ubuntu is created by a community and overseen by a corporation, but you can take the Ubuntu source and do what you want with it within the terms of Free Software. You cannot do this with OS X.
Also, your last paragraph pretty much backs up my original point: if you're going to stand on your high horse of software-freedom and write about how great it is, you better go all in. That Dell is running proprietary software; at the firmware level in the least, but probably with binary blob drivers. Oh, and the article doesn't mention (nor you) about how you have to opt-out of third party sharing of your desktop search results with Amazon! That's not freedom respecting, so please don't try to divert attention away from these very valid points with arguments about how something is forkable.