Re: AWS - too big to fail?
...and even without multi-region, AWS encourages spreading your implementation across availability zones within a single region. An 'AZ' may then often split into multiple data centres.
And there are advantages of using a 'single basket', including:
1) Optimised data transfer between different parts of the infrastructure (and it's often free too - e.g. you won't pay for data transfer between EC2 and S3 / Cloudfront) for example, which you would if the transfer hit the public internet)
2) A single set of APIs to learn, no matter which datacentre you're using.
3) If things aren't working, a single port of call in determining the issue, rather than having to deal with multiple companies all saying "not me guv"
...and if you are choosing a single 'basket', then AWS is a great choice, which is why their business is doing so well.