Looking at an excerpt in another wikipedia entry, it looks like the metric is based on phonology only:
> Demonstrates a comparative statistical method for determining the extent of change from the Latin for the free and checked accented vowels of French, Spanish, Italian, Portuguese, Rumanian, Old Provençal, and Logudorese Sardinian. By assigning 3½ change points per vowel (with 2 points for diphthongization, 1 point for modification in vowel quantity, ½ point for changes due to nasalization, palatalization or umlaut, and −½ point for failure to effect a normal change), there is a maximum of 77 change points for free and checked stressed vowel sounds (11×2×3½=77). According to this system (illustrated by seven charts at the end of the article), the percentage of change is greatest in French (44%) and least in Italian (12%) and Sardinian (8%). Prof. Pei suggests that this statistical method be extended not only to all other phonological, but also to all morphological and syntactical, phenomena.
http://en.wikipedia.org/wiki/Classification_of_Romance_langu...
Sounds rather arbitrary. Linguistics has come a long way since the 1940s, so I would take that one with a big grain of salt without confirmation from more modern references.
That said, as another comment in this subthread says, Latin survives in all Romance languages. There's no objective basis in claiming that Romanian is the one true descendant.