The ES2 uses a replaceable cable right? Maybe Westone has it down so these issues aren't a concern for them? I have no idea about UE though. Ety's cables are replaceable as well. Are there many issues with those pins? I don't know, I haven't followed the discussions at all if there have been any. I will say that my Ety's have been nearly dead for >1 year nad this is because of rips in the cable. If I could replace the cable myself, I would have a 100% working pair of Etys. I'm not thrilled about sending them to Etymotic from Canada, spending what will amount to $100 minimum because they won't sell the cables commercially. I'm still contemplating sending my pair to Drew so he can whip me up some swanky Dragon cable.
In Etymotic's defense, I've read that they do some testing for linearity once a cable is attached. I doubt this really matters much though, a cable is a cable if all made the same.
So if my cable does die on an IEM, and provided the connectors are not a wink link, I like the option, but if it is going to cause problems, screw it. Reliability is far more important to me.