I'm no engineer--I don't even play one on TV--but since we hit the 10G generation people have been telling me the passive channel--including the connectors--are key parts of the design. Their characteristics have to be considered when doing a high-speed design if you want to move data at these rates from point A to point B.
But now I will humbly stand aside and let real engineers weigh in.
I am also not an RF enginner but VLSI enginer but I agree with Anil Pandy that at 10Gbps speed we certainly need to give giid weightage to signal integrity. I am not sure about simulators we are discussing here but I do doubt if we have understood and modeled the accuracy we need to run SI at such speed?