Say my web site is based on GPL code.
AFAIK providing a service to users through a web site - even a paid service - does not violate the GPL. This is because GPL is about distribution and I haven't delivered any code. I'm providing a service and may charge for it.
However, suppose I provide an API to my web site and charge money for usage of the API.
Can one argue that in effect I've just turned my web site into a piece of sofware which I've distributed by making it a part of external software applications, thus violating the GPL?