A deliberate decision has been made to block people on unsupported platforms
Stop the drama.... they aren't "blocking you" they are just not providing the pre-compiled binaries via their auto-update mechanism past the end of the support period for people running an EOL OS. Unless you have an ink-on-paper active paid support contract from Google for this product, they don't "owe" anyone dick.
running software that otherwise would almost certainly run just fine.
That's almost certainly not true, given that all of the supporting libraries for an EOL OS also are not likely being updated. if you think there isn't a special test case, workaround, an #ifdef WIN7, etc. etc, somewhere in the giant stack of chromium + all of its dependencies, I have a bridge to sell you.
EITHER WAY, even if it ran perfectly fine today, ensuring that future versions continue "running fine" before pushing them out via an auto-update requires continued integration testing on those unsupported OS's. Because the alternative headline a few months from now is "google broke Win7/Win8 installs of chrome by pushing an untested build -or- worse!" IMHO, google is within their rights to say "this EOL OS now has x% marketshare, and x is now too small to bother paying for engineering time to continue supporting that platform"
That's where it becomes obnoxious
Running "unsupported" software IS obnoxious because the maintenance burden is now on YOU instead of the software/OS developers. Last time I checked, you can always compile your own fork of chromium on any OS you want to fool around with on your own time. "Nah, I wanted google to keep doing it for me indefinitely," is an unrealistic position in this discussion, IMHO.