IANAL so take with a grain of salt, but legal action is very rare under the GPL, and it's also expensive. In a case like this also I think it would be a tough case. I wouldn't worry about it, at least not currently.
I expect this whole discussion could have IANAL prepended to it - but it seems like an interesting question - what the licence strictly implies, beyond "It probably doesn't matter as probably nobody will take legal action against you".
Or is lack of enforcement, in the end case, the only thing that matters - making most discussions about open licences and in-depth consideration meaningless?
Or is lack of enforcement, in the end case, the only thing that matters - making most discussions about open licences and in-depth consideration meaningless?