Scott, I don't see the point of this change either.
In the beginning, we had no microcode in coreboot, per the main goal: let linux do it. We just let Linux do the update. Not our problem.
At some point, ca. 2005 or so, we had to let the blobs in because many of the new CPUs are *broken* without the microcode update: the microcode that comes embedded in the CPU must be updated or you'll get some real problems, and possibly not even get through firmware.
As you point out, this is nothing like the VGA BIOS issue.
So, sure, it's pure to build without the microcode blob, which means in reality that you're deciding to use the microcode blob *already embedded in the CPU*. And, on many new CPUs, the one that comes with the CPU has issues that mean you won't get past DRAM init. And, if you do get past DRAM init and boot, you've got a CPU that may have subtle errors and corrupt memory. Oh, joy.
I guess I don't understand why people feel better being able to build a firmware image which will boot the CPU in a broken mode.
ron