i am compiling kernels so i'm not using "pre-built". at your kind suggestion, i ran "update-initramfs -v -u -k all" (even-though it shouldn't be necessary as part of using make-kpkg); an impressive number of screens scrolled by as all my initrd.img were rebuilt (no errors). but unfortunately the result remains the same:
3.10.0-rc1 boots up just fine (finding the usual root)
3.10.0 declares it can't find the very same root (same UUID) and drops to busybox.
as much the same .config file was used to build both of these as possible (result of performing "make oldconfig" on one to get the other) ...so there has to have been some change between 3.10.0-rc1 and 3.10.0 that affects initrd.img files... i think.
the one difference as a result of running "update-initramfs -v -u -k all" being that now "file" sees only one of my kernel's associated initrd.img as being gzip, now the rest appear as: "ASCII cpio archive (SVR4 with no CRC)" ...hnnnn.