Imachuemanch: I will agree that painting is a whole other story (if may I ask kindly to see our wife's work by the way)
She doesn't have an online library - she's learning web design to make one, until then, feel free to come over, there's tea and cake in it for you ;-)
All right, your post got a bit messy there so I won't divide it into smaller bits, but I'll try to respond to the best of my ability. First of all, I'm not arguing for the way Valve is doing things. While I think both Valve and Bethesda deserve a cut, it should be nowhere as big as it is right now, 75% is just ridiculous. I'm arguing for the option of modders to sell their creations. Second, you're talking about lines of coude, models and textures here. Now there's more a bit finer points to this.
You can actually create textures and models which are 100% yours, in which case, the issue is very clearly cut - you made it, you can sell. It doesn't matter that it's just digital data, we're talking on discussion boards belonging to a website focused on selling digital data.
Then there are paid mods which use assets from freely availible ones - personally, I don't see an issue with this behaviour, as long as the paid mod builds on top of free assets from other mods and doesn't just resell them. Creator of the free mod has put his content out there for free, and while it's common courtesy to ask him whether you can use his stuff, it's always been like that.
But then there's the third possibility - use of paid content in your paid/free mod. Now I suspect things get a bit more complicated here, just as they do for the same thing in any other branch of software development. As far as I'm concerned, it's still down to common human interaction - just ask if you can do it, and if you're not allowed, you can actually get hit by copyright suit.
Now, for the most part, I can't see an issue with any of this - after all, it is how software development has worked globally for years and I only see it rapidly evolving and improving, not the other way around. I can't see why it should be any different for mods.
And that brings me to the collaborative part, to how modders share what they have made amongst themselves. It all comes down to how modders themselves handle this. From developing software on daily basis, I can see that even tho there's tons of software which requires payment before you can get it, programmers understand that collaborating and sharing their work is essential to further develop their jobs globally. Some of the biggest advancements in software industry came from need to further commercial usage and options. After all of this mess stabilizes, I can't see why mods could not end up the same way.
Oh, and as for my wife having 100% original work - no, she does not. She stands on shoulders of generations and generations of artists who were here before her and developed techniques, styles and various approaches. It's not just development of software, every human endavour gets furthered by sharing and cooperation - and while copyright laws don't exactly help, we move forward step by step every day anyhow.
At the end of the day tho, this is an innovation. Regardless of motivation behind it, it's a neutral change and I'm not smart enough to see where it'll lead. Perhaps you're correct and it'll ruin modding, or perhaps it'll lead to second gold age of it. Time will tell, but it's too soon to judge yet.
As for me, I will be cautious, wait to see how the situation unfolds, and then base my decisions on that.