The degree of insidiousness at play here by Valve and Bethesda is to such a degree I almost respect them for it. Skyrim has survived for years on mod support. I'm sure it's driven a number of game sales, but now they've found a way to profit directly off of the mod scene. And they're going about in such a way that people are actually defending them for doing so, by disguising it as "supporting the mod author." But it's not about that.
If it was about that, the author could reap the profits before $400 is made. 
If it was about that, they could have made it a donation-based system that would have netted much less fervor. 
If it was about that, the mod author would surely get a better cut than 25%. 
But it's not. It's about Valve and Bethesda making a profit from an area they previously weren't. And God bless 'em, they've found a way to do it in a way that a lot of people will actually swallow.
Fuck it, this is a great heel move. Anti-consumerism and all.