Using a mod does. These two things are in no way comparable.
Developers should be ecstatic that modders want to build off their game as a platform. It can only bring them additional money as people buy their game for access to hugely popular mod. I can understand the desire to monetize this, but too much and you freeze out your modders and you get nothing.
I feel like Arma 2 saw the Project Reality demographic and said "Lets go for that"
One wonders how that could have evolved. Someone should do experiments where they deny access to three company episodes to chimps, to see if they freak out as badly as the internet generation does when they can't get their favorite things.
75% is not to the mod developer, 75% was to Bethesda, and 25% to the mod developer.
This is what pissed people off. (Also, the developer would only get paid if he got 100 USD to receive, meaning that he needed 400 USD in sales, meaning that probably most developers would never get any money).
This all seems like an attempt to app-storify mods. I really didn't think it was a bad thing.