"unless that component itself accompanies the executable"
How do you define "accompanies"? Does every (perhaps optional) package in Debian accompany every other package, all because they came out of the Debian archive? IANAL, but it seems to me to be a stretch to interpret this clause to mean that if GNU releases glibc under LGPL3, they are intending that it would not fall under the "system component" exception.
It seems more like a subtle bug in the wording of the LGPL3 than anything else.