Someone mentioned that you can tune the transceivers to the individual cable, and that's a big part of it. Another thing is that discontinuities in the physical

Someone mentioned that you can tune the transceivers to the individual cable, and that's a big part of it. Another thing is that discontinuities in the physical layer are a big deal at these speeds (think connector). It's easier to deal with that 'inside' the plug just a short distance from the discontinuity and then have a much more reliable and predictable link between the two transceivers in the cable. Especially if the transceivers are bumping up the power significantly (I don't know if these ones are), because the discontinuities cause reflections and transmitters will be damaged if the signal reflected back at their output is too high powered. The reflections can now happen at the plug/jack interface, where it doesn't need to be so high powered because the signal will not need to travel as far.