What I find a bit interesting about that in Awesomenauts is some footage I've seen, a player will die and a teammate will actually pick up that guy's money so that it stays within the team rather than feeding the enemy. For money drops to work it seems like a mix of range and melee combat is necessary. Otherwise, like you said with Super MNC, you end up picking up a lot of your money... which seems a lot like getting rewarded for your allies dying.
Well Super MNC uses both XP and cash, although picking up cash also gives you a bit of XP. But yes, there is a bit of rewards for your own creeps dying. On the other hand, if they are dying you're probably facing off against an enemy player on the other end and you're shooting their bots at the same time. So you really do sort of both end up getting the same amount of coin that you would be getting if you were picking up the coins that came from the bots that you killed... so it pretty much evens out. If your bots aren't dying, then you're probably pushing the lane forwards, so you do get the enemy bot coin drops. It's different, but it works.
And yeah, like you said with Awesomenauts it's mostly close up fighting so you can grab the coins that drop for your teammate's death and deny them to the enemy if you're there as well. It uses no leveling at all (although characters do show a level, that's just total coin gathered divided by 100 so it's really just an at-a-glance power indicator) purely upgrades bought from the cash drops, so controlling those is a big part of the strategy.
The point being that last hit gets the gold is simply one possible way of doing this, and there's a lot of room for experimentation within the genre. If you start out with one idea and balance around it, anything could work. You could have everyone in range get xp and gold for a kill. You could have the entire team get rewarded, no matter where they are on the map. You could make enemy creep kills reward the enemy team instead of your team (that sounds insane, but both sides would have to do it or just let creeps constantly batter their towers). There's a lot of ways to experiment with the formula, and a whole lot of things besides just how you gain power to consider, and I don't think we've seen the best possible version yet by a long shot.
I'm just glad the experimentation is finally coming along. I don't know who's going to be the first MOBA version of what Half Life was for the FPS genre, suddenly making everyone realize that the formula can be twisted in all sorts of unexpected directions and become something brilliant. Or who will have the first big success with something that really bucks the trend. I was kind of hoping it would be Valve, but it appears that they plan to follow the original DOTA formula to the letter. Maybe once that's finally released they will experiment with different game modes. I can see why they're doing it standard first though, I mean Gabe could always fill a few more Olympic sized pools with money.