Jeff;
Normally it doesn't 8 weeks and, in my own experience, AWS has sped up their processing considerably compared to say, 10 to 15 years ago. What happens is test sheets are brought in from all over the world, they are then sorted into groups and scanned.
The scanning part is not "fail-safe" and it isn't unusual for the person doing the scanning to have to seek technical assistance if there are problems (the person doing the scannning isn't qualified as an inspector or necessarily even knowledgable in welding, they are clerical).
Also, the AWS Certification Department processes an enormous amount of paperwork; not just the CWI tests but also renewals, new applications, etc. The 8 weeks you are told to wait is just to allow enough time to assure your results will be back.