Their bandwidth costs would skyrocket. AWS and other cloud providers overcharge considerably on outbound transfer.
I don't think they would. Or at least, the costs would still be tiny.
Like Panic, my company mostly sells desktop apps. We're smaller than Panic, but we still have a considerable quantity of downloads each day. We use AWS S3 + AWS CloudFront to host our app downloads, and the cost is so small as to be irrelevant to my business.
S3 and Fastly (or some other very inexpensive CDN) would be fine.
My costs: $799 dedicated on 1gbps connection (overkill)
AWS Costs: $6000+
AWS is simply impossible for me.