Ratings (in the US), is the best way to measure popularity. Saying a show is incredibly popular is kind of silly if nobody really watches it. As for outside of the US, thats wide open, all i know is that they sold the series to a lot of countries.
Yes, if something costs 60 dollars its common to say "hey, it was below 1000 bucks"... If they say "below 5 million", its not likely to be 2 or 3 million. Even going by an average of 2 million, that alone is 26 mill over 13 episodes.
"Sam Raimi and Rob Tapert -- who brought us "Xena: Warrior Princess" -- and Steven S. DeKnight, who brought the world young Superman in "Smallville." Think of this series as
"Bigville" -- or at least "Big Budgetville." (
Link)
Beyond that, i cant be bothered to search for more articles, my eyes bleed from the "watch Spartacus" links
Where exactly do you have the "official number of 10-15 mill" from ? I've certainly not seen that anywhere.