WoW was spending literally tens of millions of dollars on content seen by a fraction of a percent of its player base. That was unjustifiably bad. That it continued for quite some time was a problem of the dev team culture and also, probably, a symptom that they did not have good metrics. (I have been there, done that, and got the T-shirt. Not to the tune of tens of millions but I've certainly frittered away man months on things seen by less than .1% of customers and, even worse, 0% of trial users.)
It does sound like they took it too far (I've not played WoW after losing a significant percentage of my time as a teenager to Diablo 2).
But I was talking about the general rule. I'd say that the opposite mistake is much more common amongst game developers, and it's a big reason why so many crappy games are released.
Certainly 0.1% of customers is too low. But I wouldn't call 1% too low - many of the best games ever made include lots of 1% content. And I think that's no coincidence - the mindset that results in developers putting 1% content into a game also results in a fun core game. 1% content only happens when developers care a lot about the game.
I should clarify that by 1% content I mean a different 1% of the audience will see each piece of content.
