In order to provide these statistics, some juggling of the numbers is in order; there are for instance languages with more then one localisation. A good example is Portuguese where we have a localisation that caters for the people from Brazil and one for Portugal. The "value" for these localisations is achieved by adding them up and diving by the number of localisations.
The localisation is expressed as a value from 1 to 100 and is comprised of three parts. The "most used" MediaWiki account for 40 points, MediaWiki core is another 30 points, the extensions used by the WMF is 30 points.
When you analyse these numbers, you will find that the "most used" messages are really important. This is only right because of their importance in the usability for a localisation.
What we hope for is that the real wizards will find the relation in numbers for the value of a great localisation for the popularity of our Wikipedias.. When you talk about it, it is obvious. It is however really hard to appreciate its true value.