There's logic behind the complicated rules. The idea is that you can't cause the calculated availability to go down by generating lots of requests when the service is down.
And my favourite part: "To receive a Service Credit, you must submit a claim by opening a case in the AWS Support Center." -- for a company that has built itself on automation, surely you could automate some bill credits based on the SLA.
Many companies don't give out refunds and you have to proactively request. (alas my employer's value prop, in a completely different industry of course)