EDIT: The numbers in the article below are slightly off. They assume that the new AoE kill bounty bonuses in 6.82 apply instead of the old bounties. In fact, they apply in addition to the old bounties. I am not going to try to correct these numbers now, in part because I've verified that the kill bounty messages in game do NOT properly reflect the actual amount of gold awarded to kills once the new AoE bounty is included. I also suspect that the team Net Worth graph is not properly updating to reflect the bounties, but have not verified this yet in the client. Because of this, I feel that any attempt to correct the numbers would simply lead to additional confusion. The article is still valid if you read it as applying only to the additional bonus gold granted in 6.82 rather than the total bounties. I *have* edited the response to the first question (about Lycan killing Nature's Prophet).
I would like to thank reddit user Trencha for pointing out this mistake.
Let's look at a concrete example of the new 6.82 kill bounty changes. The screenshot below was taken at exactly 16:00 on the game clock. EternalEnvy's Lycan is fighting against Buugi's Tidehunter, with Aui_2000's Dazzle (who had just cast Shallow Grave on EE) and Trixi's Nature's Prophet nearby.
Click to enlarge
Let's just suppose that Buugi and Aui_2000 are both forced away from the fight and manage to escape safely and somehow Trixi's Nature's Prophet manages to solo kill Eternal Envy's Lycan. That single kill, if it were to happen under the same game conditions in 6.82, would have a dramatic impact that could change the course of the entire game. This is due to one of the 6.82 changes that might have passed you by undetected.
The figure below shows the new formula for gold bounties for hero kills (as well as the old for comparison), the money a player receives for killing another player on the opposing team. The biggest change is that hero bounties now depend upon the discrepancy in total Net Worth across the two teams, labeled 'NWDifference' in the formula. In other words it not only takes into account the level of the victim but also the net worth of his entire team.
[swap=>>View patch notes of Bounty Changes