No such thing as killstealing in a teamgame like Demigod, the same was true for Dota, anybody who played it beyond Pubs knows that it really doesn't matter who gets the kill as long as the enemy gets killed; especially since Demigod has the relatively recent Dota feature of assists, which means you get a nice chunk of gold anyway, and I'm pretty sure the exp recieved is the same across the board.
My apologies first, as I'm about to make another Dota comparison, if only to hilight gameplay mechanics.
I think kill stealing is a little harder to stomach in Dota than it is in Demigod because of the difference in the economy mechanics in both games.
In Dota, the gold streams in at a much slower rate than in Demigod and there's no way to "upgrade" this. It's hard work farming creeps for gold with all the last hitting mechanics/jungling, so killing other heroes becomes a much more valuable source of income. This is compounded by the fact that you lose gold when your hero gets killed and even further by the dependency on items.
In Demigod, gold comes much more easily. You lose no gold when your Demigod dies (except for the loss of the stream in while you're still dead), there's no need for last hitting and you can capture gold mines or upgrade your Citadel for a greater income stream. Killing Demigods for gold becomes less vital, thus making kill stealing much more bearable. Also, there's a way to spend the gold in Demigod to explicitly benefit the entire team that's absent in Dota, so you know that a rich player on your team is still good for the team.
Demigod is also more forgiving in the items department. You don't have to totally stack your Demigod out in powerful items to contribute significantly to the team during late game. This further draws the emphasis away from needing to build personal wealth.
All in all, I've found all these elements to be more team-friendly and more enjoyable.