"The big wheel keeps on turnin... "
It makes sense. If your looking for a 'cloud' platform to develop on Amazon arguably has one of the strongest and feature rich platforms to deliver on so why not continue to round out those service offerings? Check out "Expanding the Cloud" by Werner Vogels.
Latency, security, and tooling are significant constraints of a cloud based application infrastructure. If latency is reduced by using a baked in CDN available from your 'cloud' partner, then that leaves security and tooling.
The security constraint is also more likely a mindset that "I don't physically own my data", or lack of communication on clearly stating where responsibilities start and stop, than any technical hurdle. However, the last time I looked, tools for each of the cloud platforms were coming along at a fast clip. Though, in terms of cloud computing, if you've traditionally developed for a non-Microsoft platform, you've got an advantage at the current date.
More importantly, with Amazon setting the bar so high for cloud computing, I'm extremely excited to see what other vendors will be releasing to stay competitive!