Divinity Engine is just more limited to it's own type of game.
No. The UT3 mod tools and UDK are separate. You can't use the UT3 assets in any commercial projects. UDK does come with a few built in assets that are free to use, but it's essentially an animated bi-ped and and a few meshes and textures. Basically just enough to give programmers a testing ground.
I dont know about you but last time I checked UDK had a lot of free assets including whole levels of props free to use as well a few characters, music, sound effects, pre-built scripts.
I seen Eat3D vidoes use all the ingame props to make paid Video Tutorials so I'm sure the copyright of those included assets is fine.
I support selling mods...
Completely agree with you mate, but there are people here who instead of having both options of free mods and paid mods, they DEMAND that everything stays free, they talk about people being greedy for wanting a reward but fail to see their even worse own greed, they dont want to pay but want to still have access to all contents, cheapskates is the correct word here by a mile.