I'll tell you a little story that happened around 10 years ago:
I got a call from a representative of Oracle, he asked me if we where using MySQL, and if I could described him how, because he wanted to help us make Better use of this tool.
We where pretty happy about MySQL at the time, and I went into deep details about how we used it. At the end, he told me point blank that the PHP's MySQL driver was licenced under the GPL and that we had to licence our whole codebase under the GPL since it was contaminating our code as a whole. (Even if we had encapsulated all the accesses to the driver around a single class)
The alternative was to pay the right to use it under a non GPL contaminating way.
Oracle then called and threatened us many times.
The argument that made them stop was when we told us that we where hosting the applications. This argument would not have been sufficient with the agpl.
There claim was unfonded but I can assure you that I didn't sleep well for a while!