One can both be a small indie studio and also have sold multiple millions of copies of their game. Indie simply means you don't have a publisher. And Mojan didn't.
You have to at least put a floor on that thing or you fall completely afoul of the common meaning.
My rule of thumb would be less than $1 million spent before the first public release ? (Which I assume makes Minecraft indie ?)
Now another question is whether you can even call indie those games being advertised and distributed by Steam (or any other platform) where developers are overwelmingly dependent on that platform for like 95%+ of their sales (including keys from third party websites still for that platform) - because dealing with advertisers and distributors was also an extremely important part of the job when games still came in boxes !
Indie is when the major investors are making the game, at least for me. So if the guys are making their own game without investments they are indie, as in the creators can be free of influences of outside investors.
