The Reg has no clue?
"Most the CPUs listed above are oldies that went on sale between 2007 and 2011, so it is likely few remain in normal use." is garbage and Reg authors/editors should get out in the real world.
Look at MS OS share from any source.
Look at Missing CPU types in April "Guidance" and you find PDF doesn't even cover all CPU models w/ Meltdown and Spectre problems.
Most systems running XP, Vista and Win7/8/8.1 have "old" Intel CPU and won't get a New BIOS. Most Running XP and some w/ Win7 are people down/up graded Vista systems and see little reason to replace them. Most won't buy New Intel products just to fix Meltdown and Spectre either. Note that Intel CPU bugs go back to a least Pentium FDIV bug that also never got fixed. Intel offered replacements but few knew of this and fewer bothered to get them.
Dell et al had no intention to offer BIOS updates most or all system over 2-5 years old and now have an easy way out because Intel won't bother making new MCU for most of them.
OS patches? Funny. Not. Many Win7 alone have not patch since 12-17 because MS patch failed and fix patches for that also failed. Most Linux users haven't patch for this either.