I did not say it was nonsense. I said it is not objective.
For instance, you bring up something on a mobile phone. There the text would be too small if not full screen. Something objective would state such criteria exactly and that criteria would be based on something subjective.
Obviously defining that e.g. a 4pt font is unreadable is quite easy. But when does it become readable? That is subjective. You can define e.g. 10pt and measure such a rule objectively, but rule itself ("10pt") was still based on something subjective.
I've read reviews about (IIRC) the Galaxy Tab, which is 5" or something. It also allows multiple windows (or something). Some reviews hate it (too small), some love it.
Note that GNOME is not very usable on a tablet. I suggest trying it before suggesting that it is a tablet interface.