Netflix is one of the biggest user of EWS, yet, Amazon is pushing hard on their streaming service too.
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.
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 really wish they would start pushing on each other harder, so I could use only one for both...