Morten Rand-Hendriksen has written an essay on what needs to change so that we can learn more about WordPress users to better apply the 80/20 rule when considering new WordPress features. Morten makes several points but this quote probably summarizes the tone of the article: “We can’t say we’re building solutions for the 80% because we don’t have the data to back that claim.”
Morten believes the key is to realign the WordPress project to a more user-centric approach, which would require (among other things) the need to gather large volumes of data. I've been repeatedly against most core metric gathering, because I think we can leverage host relationships to get a pretty darn accurate depiction. But I do agree (and I know the core team does too) that we need to use data to back up decision making as much as possible.