I have a set of Jubilees here, unfortunately with a bad driver. There is absolutely no carbon fiber that I can spot, anywhere. The carbon fiber "look" is from a nice paint applied to the molded plastic parts. It can and will chip off.
Before the driver had its issues (my fault - not the headhones'), it sounded smoother than the HD600 I previously owned (my biggest complaint about the HD600's sonics). Otherwise, the sound signature was essentially the same. With other brands (GRADO), I might speculate that a small-ish difference like this could be partially due to unit-to-unit variations, but all the Sennheisers I've heard have been extremely consistent (within the same model number) - that would be out of character for them.
The smoothness can be worth the premium over the HD600, for those that either prefer the HD600 over the HD650, or like them about equally. Those that prefer the HD650 signature (myself included) should stick with that. I bought a replacement set of HD650 drivers to put in the Jubilees.