Not necessarily. The fact that different cables demonstrate different behavior shows there is a good amount of wiggle room in the spec. When a new variable is added to a situation and a problem arises, that doesn't always mean it's that new variable's problem. Often the new variable is just exposing an existing problem that wasn't previously detected. This happens constantly in the software world. It's less common in hardware, as specs are usually more rigid, but it's not at all rare.
I'm not saying that's the case here, I'm just saying it's certainly possible. The cables exhibiting this issue could indeed be out of spec, but they've just gotten away with it because no popular device has been as "picky" in the past.