If amazon wouldn't have offered EWS to netflix or have stopped offering it to netflix, netflix could have easily use some other cloud competitor. Maybe netflix would had to pay a bit more , but i don't think it would have been a big difference.
I don't know much about kiva but if their service is hard to replace and is a unique competitive advantage(and looking at the purchase price,it seems so), amazon would use this advantage.Amazon is known to play hardball.
Netflix actually can't switch to an AWS competitor at this point because none of them are big enough. (source is some random cloud infrastructure presentation they did)
When AWS started they were basically running off the "christmas season" and end-of-life amazon.com boxes with almost no up front expenditures. Everyone else in the "cloud" business is buying new boxes to build out, which means its really hard for them to get to scale or handle surge loads.
I don't know much about kiva but if their service is hard to replace and is a unique competitive advantage(and looking at the purchase price,it seems so), amazon would use this advantage.Amazon is known to play hardball.