Actually, it most likely depends on the taxonomic system being used as a reference. I quoted someone else's numbers in the article. Truly, I am no taxonomist, so I have to choose my authority carefully. I trust the GRIN website's version of the APG III Taxonomic System. It lists 528 species in the Euphorbia genus and 232 genera in the family Euphorbiaceae. This is one family that has undergone tremendous changes in recent years, and there is much confusion, even among the experts, about correct names for species and exactly which plants belong in this family and which ones don't. Nobody, however, argues as to its great variety.
There are not 466 species in the Euphorbiaceae family, there are at least 10 times that many. APG III lists (about) 200 genera and 5700 species in the family. The Kew Plant List has the species count around 7500 (that's the number attached to the Wikipedia entry). Whatever your source, 466 is not the right number there. Neither is 266 (species count in Euphorbia genus)... you just said that number should be 528? Again, The Kew Plant List (and Wikipedia) list a much larger number.
My references can be found at http://www.ars-grin.gov/cgi-bin/npgs/html/taxfam.pl. I'm not talking about species in Euphorbiacea, but genera. That's a BIG difference. I have revised my numbers to reflect 232 genera in Euphorbiaceae (excluding synonyms) and 528 species (again, excluding synonyms) in the genus Euphorbia (not family, Euphorbiaceae) as listed on the GRIN website.