[thaumasiotes]

S3 isn't the name of the service - that's "Amazon Simple Storage Service". S3 is a nickname, short for "Simple Storage Service".

[eterm]

Nickname implies it's unofficial, but S3 is very much the product name too:

https://aws.amazon.com/s3/faqs/

"Simple storage service" is used once. "S3" is used throughout.

[hnlmorg]

While you’re technically correct, for all intents and purposes it is called S3 even by AWS themselves.

[anal_reactor]

When I was a student we had a Facebook group to share information, and one angry guy ranted that the correct shortening of "Mathematical Analysis" is not, in fact, "anal", as we were used to say

[rswail]

and EC2 stands for "Elastic Compute Cloud". but no one remembers that.